A Proposed Laramide Grand Canyon

Geomorphology 102 (2008) 482–495

Contents lists available at ScienceDirect

Geomorphology

j ourna l homepage: www.e lsev ie r.com/ locate /geomorph

A proposed Laramide proto-Grand Canyon

C.A. Hill a,⁎, W.D. Ranney b

a Earth and Planetary Sciences, University of New Mexico, 200 Yale Blvd., Albuquerque, NM 87123, USAb Zia Interpretive Services, 816 West Cherry Avenue, Flagstaff, AZ 86001, USA

⁎ Corresponding author. 17 El Arco Drive, Albuquerqu293 3752.

E-mail addresses: [email protected] (C.A. Hill), w(W.D. Ranney).

0169-555X/$ – see front matter © 2008 Elsevier B.V. Aldoi:10.1016/j.geomorph.2008.05.039

A B S T R A C T
A R T I C L E I N F O
Article history:
The absence of “rim grave Received 18 February 2008Received in revised form 14 May 2008Accepted 15 May 2008Available online 7 July 2008
Keywords:Grand CanyonRim gravelsCanaan Peak-type gravelsLaramide proto-Grand Canyon

ls” north of Grand Canyon and of “Canaan Peak-type” gravels south of GrandCanyon suggests that a paleocanyon, which intersected the transport of these gravels north and south, mayhave begun forming in the Laramide in approximately the same position as today's central Grand Canyon.This Laramide-age canyon is envisioned as having flowed generally from the SW to NE; from the PeachSprings Canyon area to Mile 197 where it was captured by karst; then along a N. 60°E joint system to theKanab Point area where it converged with drainage coming off the west side of the Kaibab arch. From there itflowed north along the west flank of the Kaibab arch to Paleogene Lake Claron. The critical idea suggested bythis proposed model is that the modern Colorado River utilized Laramide paleotopography in establishing itscourse through the central Grand Canyon, with younger sections of the canyon integrating with it later, in themiddle to late Miocene. This paleocanyon route, in association with headward erosion from the Grand WashCliffs toward the Kaibab arch after 16–17 Ma, helps account for the total volume of rock eroded from GrandCanyon, which cannot be explained by present-day incision rates.

© 2008 Elsevier B.V. All rights reserved.

1. Introduction

How the Colorado River established its course across Grand Canyonis one of the major problems in deciphering the Cenozoic history ofthe Colorado Plateau (Hunt, 1956). While there has been considerabledebate on the particulars of its evolution—from JohnWesley Powell upto the present day—the one general consensus is that the ColoradoRiver is remarkably independent of topographic or structural control.Early on, Dutton (1882, p. 73) made these remarks concerning thecourse of the Colorado River and its tributaries: “They run in amajority of cases against the inclinations of the strata and against thetopographical slopes. They cut through mountains and plateaus; theyenter cliffs, they emerge from them; they enter the lifts of monoclines,they cross faults from the upthrow to the downthrow. They run hereobliquely up or down the structural slopes, and there they coursealong the strike.” These, and many similar remarks made by othergeologists (Ranney, 2005), show that the Colorado River throughoutits course is not that of an old sedate river of long and normal history.Rather, the Colorado River has a complicated history, with a number offactors controlling its course.

As early as 1978, Young and McKee proposed that a Laramide-agedrainage system had flowed northward across successively higherstratigraphic units to exit in the Claron basin of southern Utah, andYoung (1982, 1987) and Beard (1996) showed this drainage as having

e, NM 87123, USA. Fax: +1 505

[email protected]

l rights reserved.

followed an approximate Hurricane monocline trend northward toUtah. Hill and Ranney (2007) proposed a more specific route for a“Laramide proto-Grand Canyon,” basing their model mainly on thetracing of gravels north of the canyon. Coevally, Flowers et al. (2007)independently proposed an almost identical “proto-Grand Canyon”based on apatite (U–Th)/He thermochronometry. The model that wepresent in this paper combines the observations of Hill and Ranney(2007) with the data of Flowers et al. (2008).

One of the main reasons why the age of Grand Canyon has been thesubject of controversy is because the different stages of Grand Canyonevolutionhave not been clearly defined.We attempt to do this inTable 1.In this paper, the term “GrandCanyon” is usedonly for a canyon inwhichthe modern, integrated Colorado River exists and which is b6 Ma. Theterms “Colorado precursor canyon” or “precursor canyon” are afterYoung (2008) and refer specifically to a western Grand Canyon thateroded headward from the Grand Wash Cliffs towards the Kaibab archbetween s∼16–6Ma (Fig.1). The term “proto-Grand Canyon” refers onlyto a paleocanyon that began forming in the area of the central GrandCanyon in the Laramide (∼40–50 Ma); i.e., it was the earliest form ofwhatwould later becomeGrandCanyon. In addition, the term “ColoradoRiver” is used for a river fully connected or integrated through thecanyon from Colorado to the Gulf of California and the term “LittleColorado River” for a river connected to the Colorado at the Confluence.The terms “ancestral Colorado River” and “ancestral Little ColoradoRiver” refer to separate river sections that existed before the Coloradobecame integrated through Grand Canyon. “Proto-Kanab Creek” refersto an early drainage parallel tomodern Kanab Creek along thewest sideof the Kaibab arch, but at a higher elevation and flowing in the oppositedirection.

mailto:[email protected]

mailto:[email protected]

http://dx.doi.org/10.1016/j.geomorph.2008.05.039

http://www.sciencedirect.com/science/journal/0169555X

Table 1Terminology used for the stages of Grand Canyon evolution over time

Term Area Time Term introducedby

Grand Canyon (Cañon) Entire Grand Canyon afterColorado River integration

b6 Ma Powell (1875)

Precursor canyon orprecursor Colorado canyon

Western Grand Canyon;east of Grand Wash fault and

∼16–6 Ma

Young (2008)

Proto-Grand Canyon west of kaibab archCentral Grand Canyon;from about Mile 90 to 225

∼40–50 Ma

Hill et al., (2008)Flowers et al.(2007)Hill and Ranney(2007)

Fig. 2. Schematic cross section of the stratigraphy of Grand Canyon. The proposedLaramide proto-Grand Canyon incised through this entire sequence of rock strata—fromPrecambrian to Mesozoic—as it cut northward toward the Early Tertiary lakes of Utah.Black areas show the stratigraphic position of caves in the Redwall–Muav aquifer, thecircles show the gravels of the Shinarump Member of the Chinle Formation.

483C.A. Hill, W.D. Ranney / Geomorphology 102 (2008) 482–495

We recognize the inherent speculative nature of some of ourinterpretations, but present new data on the curious distribution ofdifferent gravel types north and south of Grand Canyon. We acceptthat some parts of our conclusions may evolve as we, or futureworkers, synthesize newer data. However, many previously presentedmodels for the enigmatic evolution of the Colorado River and GrandCanyon began with bits of data that were supported by speculationsand proposals—some even that were deemed as “outrageous” (i.e.,Hunt, 1969), but which nevertheless benefited, were expanded upon,or accepted by other workers. Therefore, in the spirit of these boldattempts, we present the current work.

2. Regional setting

2.1. Geomorphology

Grand Canyon of NW Arizona (Fig. 1) is located within theColorado Plateau Province of western North America. It occupies aregion of broad continental crust. The overall physiographic settingof the region is one of plateaus and canyons characterized by an aridto semiarid climate. The stratigraphic section exposed by GrandCanyon is over 1.6 km (1 mi) deep and consists of rocks ofProterozoic to Mesozoic age (Fig. 2). Elevation of the Colorado Riverat Mile 0 (Lees Ferry) is 960 m (3116 ft) and at Lake Mead (Mile 235)it is 353 m (1157 ft), which provides an average gradient of 2.5 m/km(8.3 ft/mi).

Fig. 1. Grand Canyon of northern Arizona, USA. The rectangle denotes the area that encompextends from about Miles 130 to 240, the “eastern proto-Grand Canyon” extends from about130 to the Bryce Canyon area. LF=Lees Ferry, C=Confluence, DV=Desert View, GV=GrandvieLGG=Lower Granite Gorge. The numbers refer to river miles from Lees Ferry.

Most of the tributaries draining into the Colorado River along itsGrand Canyon section are intermittent; where flow is perennial, it issupplied by groundwater (spring) discharge. The aquifer system inGrand Canyon is—and has been for millions of years—karstic. Theprimary water-bearing unit is the Redwall–Muav aquifer, where the

asses the proposed Laramide proto-Grand Canyon. The “western proto-Grand Canyon”Miles 90 to 130, and the “northern proto-Grand Canyon” extends northward from Milew monocline, CJ=Crazy Jug monocline, S=Supai monocline, UGG=Upper Granite Gorge,

484 C.A. Hill, W.D. Ranney / Geomorphology 102 (2008) 482–495

Redwall and Muav limestones behave as a single hydrostratigraphicunit. The Redwall–Muav aquifer contains many caves, both ofunconfined (vadose) and confined (artesian, phreatic) types (Huntoon,2000; Fig. 2).

3. North Rim and South Rim gravels

The location of gravel remnants on the plateaus north and south ofGrand Canyon is shown in Fig. 3. “South Rim gravels” are those southof the Colorado River that have a traceable source from the south.“North Rim gravels” are those north of the Colorado River that have atraceable source from the north.

3.1. South Rim gravels

In the Late Cretaceous to Eocene, rivers that flowed north tonortheast from the Mogollon Highlands deposited a series of gravels

Fig. 3. Schematic drawing showing geographic features and place names relative to the locagravels” of Koons (1964) and Scarborough et al. (2007). “Young's channels” are those of YoSprings Canyon, and other smaller canyons to the east. The solid yellow areas denote “Canadirection of transport of these gravels. Note that no South Rim rim gravels (red) have beenfound south or east of the Colorado River. JC=Johnson Creek, CK=Cedar Knoll, LCK=Little CCorral, WP=Wire Pass, WH=White House, DB=Dive Butte, CM=Cedar Mountain, BH=Bushgravels are of problematic origin and are discussed in the text.

over the Mogollon slope almost all the way to where Grand Canyonexists today. These so-called “rim gravels” formerly buried much ofnorthern Arizona beneath 100 m (300 ft) or more of sediment (Young,2001). Holm (2001) made an attempt to classify gravels in northernArizona based on their stratigraphic position and composition,referring to “rim gravels” as “distant plateau gravels.” These gravelswere deposited over a widespread erosion surface that had developedon the Hualapai and Coconino Plateaus in Late Cretaceous or earlyPaleocene time. This erosion surface cut down to the resistant KaibabLimestone on the Coconino Plateau, but to deeper stratigraphic levelson the Hualapai Plateau. In the area of “Young's channels” (Fig. 3), rimgravels fill paleocanyons incised to Precambrian rock in parts of PeachSprings Canyon and to the Cambrian Tapeats Sandstone in Hindu andMilkweed Canyons (Fig. 4).

Rim gravels are composed of coarse sedimentary (limestone,chert), metamorphic, and igneous (volcanic and plutonic) debriseroded from Precambrian and Paleozoic rocks of the Mogollon

tion of South Rim and North Rim gravel remnants. The solid red areas denote the “rimung (2001) denoting rim gravels exposed along Milkweed and Hindu Canyons, Peachan Peak-type” gravels coming down from the north. The arrows point in the presumedfound north of the Colorado River and no Canaan Peak-type gravels (yellow) have beenedar Knoll, GN=Goosenecks, WK=West Kaibab arch, EK=East Kaibab arch, KC=Kitchenhead Knoll, HR=Horse Ridge, NN=No-Name Knoll. The Grassy Mountain and Wupatki

Fig. 4. Generalized cross section of the Laramide-age paleochannel exposed byMilkweed Canyon, Hualapai Plateau, showing four of the rim-gravel units. Note that this paleochannelincised down to the stratigraphic level of the Tapeats Sandstone. From Young (2001). “From Colorado River: Origin and Evolution, edited by Richard A. Young and Earle E. Spamer.Reprinted by permission of the Grand Canyon Association.”


Highlands to the south of Grand Canyon and from the Kingman upliftarea to the west and southwest of Grand Canyon (Fig. 5). Thickness ofthe rim gravels varies from a thin veneer (lag gravels) up to thickpaleocanyon deposits. The rim gravels preserve and document theexistence of paleovalleys up to 1.6–4.8 km (1–3 mi) wide, eroded460 m (1500 ft) into the plateau surface within 13 km (8 mi) of theColorado River gorge (Young and Brennan, 1974).

The rim gravels of the Hualapai and Coconino Plateaus have beenassigned a late Paleocene to middle Eocene age based mainly on thepresence of various types of gastropods (Viviparus, Physa, Liolpacodes),charophytes (Gyrogona), and ostracods (Bisulcocyridea) found in thelacustrine Westwater Formation on the Hualapai Plateau (Fig. 4) andin the Long Point Limestone on the Coconino Plateau (Young, 2001;Fig. 5). These gastropods are similar to those of Paleocene–Eocene agefound in the Claron Formation of SW Utah (Goldstrand, 1994).However, Cather et al. (2008) recently challenged this assigned agefor the rim gravels by questioning whether the stratigraphic range ofthese fossils was limited to the late Paleocene to middle Eocene.Instead, these authors suggested a possible rim gravel age of lateEocene to early Oligocene. The primary paleontological basis fordating these deposits seems to be the charophytes and whether theycan be identified as to species, which restricts the rangemore than thegenus (J. Eaton, Weber University, personal communication, 2008). Atpresent, the age of rim gravels is controversial and is still beingresolved.

Another possible rim-gravel site occurs on the South Rim east ofthe San Francisco volcanic field in the Wupatki area (Fig. 3). TheseWupatki gravels are present in the “Doney Channel” of Breed (1969),who was of the opinion that the sinuous channels were Pliocene inage. Elston and Young (1991) assigned a Laramide (rim-gravel) age tothe Doney Channel gravels; however, Holm (2001) thought thatinstead of being rim gravels, they were lag gravels from the basalShinarump Member of the Chinle Formation (Fig. 2). Hill et al. (2006)agreed that these gravels aremainly of Shinarump origin, but they alsofelt that a small percent of rim-gravel material (perhaps reworked)could be mixed in with Shinarump clasts.

3.2. North Rim gravels

The investigations of Hill et al. (2005) and Scarborough et al.(2007) have systematically traced the transport of quartzite gravelsalong a fluvial system fanning southward and eastward from the BryceCanyon area (Fig. 3). These are called “Canaan Peak-type gravels”because they either derived directly from the Late Cretaceous CanaanPeak Formation (Fig. 6) or from the basal member of the Eocene ClaronFormation, which is composed of reworked Canaan Peak material.

The age of deposition of the Canaan Peak-type gravels in theirpresent position (Fig. 3) is not Paleocene–Eocene, as is probable for therim gravels. Rather, they were deposited sometime after a drainagereversal—perhaps starting in the Oligocene and continuing up to thepresent along modern streams. Absolute ages have not beendetermined for these Canaan Peak-type deposits, but relative agescan be estimated based on the occurrences of these gravels and theirelevations. We assign a Laramide age to a proto-Grand Canyon basedonly on the rim gravels and not on the Canaan Peak-type gravels.However, the basic idea is that if there was already a proto-GrandCanyon present in the Eocene, it would have blocked gravel transportsouthward in the Oligocene and after; thus, the distribution of thesenorthern gravels still indicates that an early canyon had to have beenin place.

Canaan Peak-type gravels consist of colorful, rounded to wellrounded, pebble- to cobble-sized, quartzite clasts, a number of whichdisplay percussion marks indicative of powerful stream action. Thesedeposits consist mainly of lag gravels (e.g., Fig. 7) from which littlepaleocurrent information can be gleaned; however, these gravelscould only have been derived from the north based on theirprovenance. Canaan Peak-type gravels differ from rim gravels in thatrim gravels consist of many rock types (sedimentary, metamorphic,igneous) that are often bedded and cemented, while Canaan Peak-type gravels are almost exclusively composed of unconsolidatedquartzite clasts of pebble size up to cobbles 25 cm (10 in) or more indiameter. These gravels can also be differentiated from Shinarumpgravels in size and composition: Shinarump clasts usually being b6 cm

Fig. 5. Schematic drawing showing the route of the proposed proto-Grand Canyon in Laramide time. Black arrows show the direction of proposed flow. Red words denote the level towhich this paleocanyon incised. The “barbed tributaries” are those off both the east and west sides of the Kaibab arch that are obtuse to the direction of today's drainage. UGG=UpperGranite Gorge, H-MW=Hindu-Milkweed Canyon, PS=Peach Springs Canyon, DC=Diamond Creek. Monoclines after Huntoon et al. (1996).


(2 in) in diameter andmore variable in composition. Canaan Peak-typegravels are very resistant and have endured at least two to three cyclesof erosion. Goldstrand (1990) traced the original source of thequartzite clasts in the Canaan Peak Formation to the MississippianEleana Formation of southern Nevada.

Over 70 gravel sites have been visited so far in a 6-year gravel studyof the Grand Canyon area (Scarborough et al., 2007). Sites related tothis paper are shown in Fig. 3 (from west to east): Johnson Creek,Cedar Knoll, Little Cedar Knoll, Goosenecks, west Kaibab arch, eastKaibab arch, Wire Pass (Fig. 7), Kitchen Corral, White House Ruins,Dive Butte, Cedar Mountain, and three sites on the Paria Plateau(Bushhead Knoll, Horse Ridge, and No-Name Knoll). Remnants ofthese Canaan Peak-type gravels have been observed on topographichighs from 2320 m (7600 ft) elevation on the west side of the Kaibabarch to 1800 m (5890 ft) elevation on Cedar Mountain. They are alsobeing transported southward and eastward along the present-daystream channels of Kanab Creek, Paria River, and Escalante River.Along the flanks of the Kaibab Plateau, Canaan Peak-type residualgravels were deposited over a Kaibab Limestone surface, but on theParia Plateau and north and east of the Kaibab arch they weredeposited on Mesozoic-rock surfaces (Fig. 7).

One other north-rim gravel occurrence is found at GrassyMountain directly overlain by the ∼6 Ma Grassy Mountain basalt(Fig. 3). These Grassy Mountain gravels are controversial butimportant because, according to Lucchitta and Jeanne (2001), theage of the western Grand Canyon partly depends on their proper

interpretation. Lucchitta and McKee (1975) first proposed that theGrassy Mountain gravels were rim gravels transported from the southacross a continuous Hualapai–Shivwits Plateau just before 6 Ma. Thisinterpretation means that the entire Grand Canyon (both the easternand western sections) could not have existed before 6 Ma. Lucchittaand Jeanne's (2001) b6 Ma interpretation, however, is in conflict withthe observations of Faulds et al. (1997, 2001), Wallace (1999), Young(2001), Polyak et al. (2008), and Young (2008) who favored an olderwestern Grand Canyon.

Scarborough et al. (2007) collected clasts from the west side ofGrassy Mountain and found them to be mostly composed of residualShinarump or other pieces of local derivation. A very small percentageof these gravels were found to be exotic clasts of Tapeats Sandstone,granite, and quartz-biotite schist. These exotic clasts are subangular intexture and so were probably not transported very far. An alternativeinterpretation to that of Lucchitta and Jeanne (2001) is that theKingman uplift/Gold Butte area could be the source of these clasts(Fig. 3). Beard (1996) placed the unroofing of the Gold Butte granite atN16 Ma and thought that the entire Paleozoic section was most likelyeroded from part of the Gold Butte block prior to extension. Beard(1996) also showed the Shivwits scarp of Young (1985) in a positionsouth of the northern Gold Butte block. Therefore, it is notunreasonable that the unroofing of the Cambrian Tapeats Sandstoneand Precambrian granite/biotite schist exposed in the northern part ofthe Gold Butte area could have supplied these clast types eastward toGrassy Mountain (Fig. 3)—most likely sometime before 16 Ma, after

Fig. 7. Wayne Ranney inspecting the Canaan Peak-type lag gravels at Wire Pass, just atthe intersection with Kaibab Gulch before it turns into Buckskin Gulch. The gravelsoverlie the Jurassic Navajo Sandstone. Photo by Carol Hill.


which time Basin and Range faulting would have disrupted thetransportation of these gravels. In this scenario, a continuousHualapai–Shivwits Plateau is not necessary for the deposition of thegravels at Grassy Mountain, and therefore, Lucchitta and Jeanne's(2001) interpretation for the western Grand Canyon having to beb6 Ma is not required. We propose that no south-derived gravels existnorth of the Colorado River.

The most important thing to note about the distribution of gravelsin Fig. 3 is that none (with the possible exception of the questionableGrassy Mountain gravels) crossed the Colorado River coming from thesouth and none crossed the Colorado River coming from the north.This distribution suggested to Hill and Ranney (2007) that apaleocanyon—in approximately the same position as today's centralGrand Canyon—had intersected the transport of gravels both from thenorth and from the south.

4. The “Early Tertiary proto-Grand Canyon” of Flowers et al.

Flowers et al. (2007, 2008) used apatite (U–Th)/He dating toconstrain the development of significant relief and patterns ofregional exhumation for the Grand Canyon region of the southwesternColorado Plateau. (For an explanation of this dating method refer toEhlers and Farley, 2003.) Flowers et al. (2008) obtained data fromPrecambrian crystalline basement samples collected from LowerGranite Gorge in the western Grand Canyon and Upper GraniteGorge in the east-central Grand Canyon (Fig. 1, LGG and UGG); fromthe Permian Esplanade and Coconino Sandstones and TriassicMoenkopi Ssandstone (Fig. 2); and from rim gravels collected fromthe FrazierWell, Long Point, and Blue Mountain areas (Fig. 3). The two

Fig. 6. In situ quartzite cobbles of the Canaan Peak Formation, Powell Point, southernUtah. These resistant cobbles were shed westward to form the basal member of theClaron Formation, and later in time they were reworked toward the south and east bydrainages flowing toward a proto-Grand Canyon or ancestral Little Colorado River.Height of cliff face is about 12m (40 ft); length of longest cobble (lower right of photo) isabout 30 cm (1 ft). Photo by Doug Powell.

most important results of this dating effort, relative to an EarlyTertiary proto-Grand Canyon, are:

(i) A paleocanyon incised down to the Tapeats/Precambrian levelexisted in the Meriwitica, Hindu, Milkweed, and Peach SpringsCanyon sections of the western Grand Canyon in the Paleo-cene–Eocene. By 50–30 Ma, these paleocanyons had at leastpartly filled with rim gravels.

(ii) In the Upper Granite Gorge section of the east-central GrandCanyon, another significant paleocanyon had incised into post-Paleozoic strata by the early Eocene. Significant incision ofGrand Canyon below Kaibab level then did not occur untilsometime after 23 Ma.

5. The “Laramide proto-Grand Canyon” of Hill and Ranney

We now expand on the Laramide proto-Grand Canyon proposed byHill and Ranney (2007) and apply the findings of Flowers et al. (2008)to this model (Fig. 8). We begin in the “western proto-Grand Canyon”(Miles 240 to 130; Fig. 1), going opposite to the flow of today'sColorado River, then proceed to the “eastern proto-Grand Canyon”(Miles 90 to 130), and then finally to the “northern proto-GrandCanyon” (Mile 130 to the Bryce Canyon area). For each section, anexplanation is given as towhy a proto-Grand Canyon took the course itdid as it cut northward over progressively younger rock (Fig. 5).

5.1. Western proto-Grand Canyon

5.1.1. Hualapai Plateau paleocanyonsThe depth to which paleocanyons incised into the Hualapai Plateau

in the Laramide has been amply documented by Young (2001) and innumerous other of Young's publications. The Hindu–Milkweedpaleocanyon, which cut down to Tapeats level (Fig. 4), confluencedwith the Peach Springs paleocanyon near today's Diamond Creek(Fig. 5). At this time a 365–450 m (1200–1500 ft) high, NW–SEtrending Eocene scarp composed of upper Paleozoic strata just northof Hindu-Milkweed Canyon (Young, 1985; Fig. 5) existed, with thisscarp directing drainage from the Kingman highlands along its SEtrend. The Kingman arch is Laramide in age (Lamb et al., 2005), buthow much Paleozoic/Mesozoic overburden covered this arch inLaramide time is uncertain. Flowers et al. (2008) identified a singlephase of Sevier–Laramide unroofing along this part of the ColoradoPlateau margin at N60 Ma, with denudation to the Kaibab surface bythe time of rim-gravel deposition at ∼50 Ma, so probably much to all

Fig. 8. The exhumation of the Grand Canyon region based on the apatite (U–Th)/He thermochronometry data of Flowers et al. (2008). Reconstructed sedimentary thickness (boldlines) are for 80 Ma, or just before the Laramide orogeny; 50–30 Ma, or during and just after the Laramide orogeny; 16 Ma, or when the western Grand Canyon began to headwarderode from the GrandWash Cliffs; and 0 Ma, or what is present-day topography. Dashed lines represent contacts between major rock units of different age. Hindu-Milkweed Canyonwas excavated in the Laramide (50 Ma), but Lower Granite Gorge was not excavated until b16 Ma along the retreated Shivwits scarp. Vertical exaggeration is 25×. Modified fromFlowers et al. (2008).


of the overburden on the Kingman arch had been removed by thistime.

5.1.2. Hurricane monocline to N 60°E sectionWe propose that a Laramide proto-Grand Canyon headed north

from the Peach Springs paleocanyon following structure approxi-mately parallel to the Hurricane monocline. It incised down-gradientbut up the stratigraphic section because the NE regional dip exceededthe gradient of the river flowing in the paleocanyon (Fig. 5). Along thissection, as the paleocanyon progressively incised northward, iteventually encountered the Redwall Limestone, at which time theRedwall–Muav aquifer would have been brought near river level. Thetruncation of this aquifer by canyon incisionwould have then suppliedcarbonate-rich water (as springs) to the flow.

The channel of the Colorado River (in the paleoflow direction) doesnot directly follow the Hurricane monocline but trends to the westand north away from the Hurricane monocline to parallel the LoneMountain monocline until about Mile 197. From there, it takes anabrupt turn to the east, crossing the Lone Mountain anticline andmonocline as well as the Hurricane monocline/fault. From Mile 190 itgoes NE, following a consistent trend all the way to Kanab Point(Fig. 9).

What factors might have caused the abrupt turn of a proto-GrandCanyon from north to east and then to take this consistent course for adistance of 75 km (46 mi)?

The change in direction of a proto-Grand Canyon fromnorth to eastalong the Lone Mountain anticline, Lone Mountain monocline, andHurricanemonoclinemay have been due to karst factors. For any karstaquifer system, the movement of water is dependent on a hydraulicgradient betweenwhere the water recharges and where it discharges.If this basic condition is met, then flow in a karst aquifer can readilycross faults and folds, move opposite to dip, or go under or throughstructures as it pursues a path along the steepest hydraulic gradient todischarge at springs (Huntoon, 1995). Specifically for the GrandCanyon area, springs are localized along such faults/fractures and/orstructural lows where the Redwall–Muav aquifer is exposed orconnected to the surface (Huntoon, 2000).

If fractures were present in the Redwall Limestone along the LoneMountain anticline/monocline and Hurricane monocline, as they arealong the Palisades Creek branch of the East Kaibab monocline(Reches, 1978), then these fractures could have provided thepermeability along which water could have traveled under thesetopographic features to emerge as carbonate-rich springs along thesynclinal low of the Hurricane monocline. Or, as stated by Ford andWilliams (1989, p. 149–150): “Joints are most readily penetrated bypercolating waters when under tension; thus anticlines (and domes)are potentially important sites for aquifer recharge. On the other hand,synclinal troughs favor flow convergence and the accumulation ofgroundwater.”

We propose that the trend of the Colorado River from the base ofthe Hurricanemonocline to Kanab Point was determined by structure:

(i) SW–NE compression was initiated during the Laramide and, byinference, extension occurred perpendicular to this direction atSE–NW. This extension would have created joint patterns thattrend SW–NE, and therefore a paleocanyon river could havefollowed this NE-trending Laramide joint system.

(ii) The N60°E trend in this section of Grand Canyon also closelyparallels the J1 joint trend of Roller (1989), which is the maincave-bearing joint in the Mississippian Redwall Limestone. Forexample, in the western Grand Canyon the Main Passage ofGrand Canyon Caverns trends about N 50°E, themain passage inDiamond Cave trends N 57°E, and a number of parallel passagesin Corkscrew Cave trend about N 50°E (Fig. 9).

(iii) A general N 50–60°E regional trend of structural lineaments inthe western Grand Canyon exists from the Virgin Riversouthward to the area around Diamond Creek (Fig. 9). Lucchitta(1975) plotted these NE-trending lineaments in both thewestern Grand Canyon and adjacent Basin and Range. Thus,this section of the Colorado River could have followed a NElineament created in an extensional stress field of Basin andRange age.

Most likely all three of these NE structural trends relate to evenearlier stress forces that set a NE pattern or grain to the central Grand

Fig. 9. The western Grand Canyon region showing the main NE-trending lineaments of Lucchitta (1975). (1) NE-trending faults in the down-dropped Basin and Range,(2) approximate boundaries of “anomolous belt” of closely spaced graben and no volcanic centers, (3) other NE lineaments visible on ERTS photos, and (4) the section of the ColoradoRiver from about Mile 197 to Kanab Point. The section of the Virgin River from Mesquite, NV, to Hurricane, UT, also parallels the NE lineament trend of the western Grand Canyonregion, as do cave passages in the region. LGG=Lower Granite Gorge, PSC=Peach Springs Canyon, DC=trend of the main passage in Diamond Cave, GCC=trend of Main Passage inGrand Canyon Caverns, CSC=trend of a number of passages in Corkscrew Cave, Hmf=Hurricane monocline/fault, Tf=Toroweap fault, LMa=Lone Mountain anticline, LMm=LoneMountain monocline. Modified from Lucchitta (1975); structure from Wenrich et al. (1997).


Canyon region. During times when NW–SE extension prevailed, NE-directed joints and lineaments were formed along these former zonesof weakness. Considering the necessary Laramide age of the proposedpaleocanyon, the combined first and second options are favored asdefining the N 60°E trend of a paleocanyon from about Mile 190 toKanab Point at Mile 145 (Figs. 1 and 9).

Our karst model for this section of the proposed Laramide proto-Grand Canyon is as follows. Somewhere around Mile 197 our north-flowing paleocanyon river was captured by a sinkhole/joint system inthe Redwall Limestone and most of this water was diverted under-ground toward the east. This karst groundwater moved to discharge asa series of springs along the base of the Hurricane monocline.Subsequent collapse and incision along a NE Laramide extensionaljoint system then “set” the direction for a proto-Grand Canyon all theway to Kanab Point (Fig. 9).

So where are the caves that testify to this proposed karst diversionof a proto-Grand Canyon river? Three cave entrances can be seen inthe east wall of the Redwall Limestone high above the Colorado Riverat Miles 200, 201, and 203, but these are probably artesian cavesunrelated to a Laramide karst diversion. We propose that collapse andincision along a karst diversion probably caused the route nowoccupied by the section of Grand Canyon between Mile 197 and Mile190. Any caves that may have once existed in the recharge anddischarge zones of this former karst system have probably beenobliterated by erosion and/or by later Basin and Range-age movementalong the Parashant Canyon and Hurricane faults, respectively.

According to the geologic map of Wenrich et al. (1997), theelevation near the top of the Redwall Limestone (i.e., the MooneyFalls, cave-bearing member, Fig. 2) at Miles 205–197 is ∼975 m(3200 ft), whereas along the synclinal axis of the Hurricanemonocline it would have been (before erosion of the surroundingcliffs) at ∼850 m (2800 ft). Over a distance of ∼10 km (6 mi) fromrecharge to discharge, this would amount to a hydraulic gradient ofabout 0.0127, which would have been more than sufficient to movekarst groundwater under the Lone Mountain anticline/monoclineand Hurricane monocline. We propose that this karst diversiondirected the course of the paleocanyon river from north to east, in asimilar manner as Hill et al. (2008) proposed that the Colorado Riverchanged direction from south to west across the Kaibab arch nearDesert View ∼6 Ma (DV, Fig. 1).

5.2. Eastern proto-Grand Canyon

5.2.1. Kanab PointThe N 60°E-trending section of Grand Canyon goes from about

Miles 190 to 145 (paleoflow direction). At Mile 145, Kanab Creekconfluences with the Colorado River (Figs. 3 and 9), which junctionmarks the northernmost extent of the Colorado River in the main partof Grand Canyon. Our “eastern proto-Grand Canyon” does not begin atKanab Point but at Mile 130—or about 15 km (9 mi) east of KanabPoint, just before the modern canyon veers to the SE and encountersPrecambrian rock in Upper Granite Gorge (Fig. 1).


At Kanab Point, we envision a Laramide proto-Grand Canyonincising down only to about Kaibab level. The logic behind thisplacement involves the Eocene to Oligocene(?) Long Point Limestone,which directly overlies the Kaibab Limestone south of Grand Canyon(Fig. 5). If a proto-Grand Canyon had incised much deeper than Kaibablevel, then Lake Long Point would have drained into this paleocanyon.Conversely, if a Laramide paleocanyon river was at amuch higher levelthan the Kaibab, it would have drained into Lake Long Point ratherthan flowing north into the Claron basin.

5.2.2. Upper Granite GorgeThe basis for Flowers et al.'s (2008) conclusion that a “proto-Grand

Canyon” in the Upper Granite Gorge region had been carved in post-Paleozoic rock during Paleogene time is that Upper Granite Gorgebasement rocks and the Esplanade and Coconino rocks (N1200 mstratigraphically higher) have similar apatite cooling temperatures.This implied to them that a paleocanyon existed along the present-dayUpper Granite Gorge in the Laramide. The data of Flowers et al. (2008)indicated that by Eocene time Upper Granite Gorge had incised downas far as Triassic/Jurassic rock (Fig. 8).

Flowers et al.'s (2008) data agreewithwhatwe have proposed for aLaramide proto-Grand Canyon in the Upper Granite Gorge section ofthe canyon (Hill and Ranney, 2007). According to this model, drainageoff the southwestern part of the Kaibab arch was constrained alongthe synclinal axis of the steep Grandviewmonocline, and then furtherconfined between the Crazy Jug and Supai monoclines (Fig. 5).Because the Kaibab archwasmost likely still covered byMesozoic rockat this time, a paleocanyon would have incised northwestward, downthrough this Mesozoic rock, before reaching to about Kaibab level inthe stretch between Mile 130 and Mile 145.

5.3. Northern proto-Grand Canyon and Lake Claron

5.3.1. Proto-Kanab CreekOur “northern proto-Grand Canyon” does not begin at Kanab Point

but somewhat farther east at Mile 130, starting at about KaibabLimestone level and then incising northward up-strata into Mesozoicrock. This position takes into account the Mesozoic landscape thatprobably existed over the Kaibab arch in the Laramide. Reasonably aproto-Grand Canyon river should have followed the “hinge” or strikevalley between the flank of the arch and a Mesozoic plateau terrain tothe west. We have placed a “proto-Kanab Creek” about 15 km (9 mi)east of today's Kanab Creek (Fig. 5).

A number of creeks/canyons off the west side of the Kaibab archhave a NW drainage pattern: Lookout Canyon, Oquer Canyon,Moquitch Canyon, and smaller canyons to the north of MoquitchCanyon. These older canyons have been beheaded by youngercanyons heading SW into Grand Canyon or Kanab Creek.We considerthese NW-trending sections of canyons to be “barbed tributaries”that could have drained into a proto-Kanab Creek when this creekflowed north toward Lake Claron. Barbed drainage is wheretributaries flow into a river at an obtuse angle to today's flow,suggesting a past reversal of drainage. We propose that barbed flowoccurred off the west side of the Kaibab arch as well as off the eastside of the Kaibab arch; e.g., South Canyon, North Canyon, and RiderCanyon (Ranney, 1998; Fig. 5).

The elevation at which a “northern proto-Grand Canyon” flowednorthward to Lake Claron is not certain, but it would have been higherthan the 2320m (7600 ft) Canaan Peak-type gravels found today alongthe west side of the Kaibab arch (Fig. 3, WK, 7600'). These are thegravels mapped by Billingsley (1992) as Tg in the NE corner of hisJumpup map and represent Canaan Peak-type gravels coming southfrom the Bryce Canyon area sometime after a drainage reversal. Thesegravels were observed by Scarborough et al. (2007) at elevations ofbetween 2250 and 2290 m (7400–7500 ft), and they do not extendhigher than 2320m (7600 ft) along thewest side of the Kaibab arch (G.

Billingsley, USGS, personal communication, 2007). Karlstrom et al.(2007) proposed 750–900 m (2460–2950 ft) of elevation rise fromNeogene surface uplift of the Colorado Plateau; if this is the case, thenthe Laramide elevation of this north-flowing paleocanyon river wouldhave been roughly at about 1500 m (5000 ft) asl.

5.3.2. Lake ClaronAfter traversing high along the west side of the Kaibab arch, we

have a northern proto-Grand Canyon river flowing into Lake Claron insouthern Utah (Fig. 5). The Paleocene–Eocene Claron Formation is afluvial to shallow lacustrine limestone. It contains a basal conglom-erate unit, which consists mainly of reworked Canaan Peak quartzites;a Pink Member, which is a pink-colored, thick-bedded, clasticlimestone; a White Member, which is a light-gray, dense, massivelimestone; and a Variegated Sandstone Member, which consists ofsandstone, siltstone, mudstone, and sandy limestone (Goldstrand,1990). Gastropods (Viviparus, Goniobasis, Physa) of late Paleocene–Eocene age have been identified in the Claron, and it is generallyconsidered to be of this age (Goldstrand, 1994; Eaton and Hutchinson,1995). Paleocurrent data from the Claron indicate incoming flow intothe lake from the northwest, north, and northeast; but another sourceof sediment may have been the uplifted regions of northern Arizona,which most likely formed the southernmost boundary of the Claronlake basin (Goldstrand and Eaton, 2001).

What is the source of carbonate for the limestone of the ClaronFormation? We suggest that one possible source could have been aproto-Grand Canyon river that emptied into Lake Claron, carryingwithit a high amount of dissolved carbonate derived from the progressivetruncation of the Redwall–Muav aquifer by our paleocanyon. Evidencefor at least a partial source of carbonate from the Redwall aquifer arethe strontium isotope ratios (87Sr/86Sr) obtained on samples wecollected from the Pink andWhite Members in the Bryce Canyon area.Strontium isotope values for the Pink and White Members of theClaronmeasured0.710424, 0.711472, and0.70923 (n=3,mean=0.71038,this study); while values for speleothems deposited from Redwallkarst aquifer water measured 87Sr/86Sr=0.712106–0.723185, n=8,mean=0.714598 (V. Polyak, University of New Mexico, personalcommunication, 2008). The strontium values for the Claron Forma-tion may reflect an input from the Sevier thrust zone to the west, asmodeled by Gierlowski-Kordesch et al. (2008). However, alsopossible is a proto-Grand Canyon river that could have suppliedhigher strontium-ratio carbonate to the Claron Formation in itssoutheastern part (wherewe sampled). If the higher strontiumvaluesof Redwall aquifer water are mixed with Kaibab Limestone values(∼0.709; Monroe et al., 2005), then the intermediate 87Sr/86Sr valuesmeasured for the Claron may reflect a contribution of a proto-GrandCanyon drainage system into the Claron basin.

6. Post-Laramide geomorphology

6.1. ∼35–6 Ma

6.1.1. Drainage reversalThe north-flowing regional drainage pattern continued through

the Eocene and into the Oligocene, but then Basin and Range down-warping caused a back-tilting and down-dropping of strata toward thesouth and west and a reversal of drainage from north- to south-directed. According to Young (1987), a 0.5° to 1.0° increase of regionaltilting toward the south could have created a 1500–3000 m (∼5000–10,000 ft) elevation reversal, so that the southwestern edge of theColorado Plateau was lowered relative to the southern Utah–Claronarea. Young andMcKee (1978) estimated the time of this reversal to be∼25 Ma (minimum age); but this change in hydrologic regime musthave taken place very gradually, probably during the Oligocene.

We place the location of a south-flowing river out of the Claronbasin after a drainage reversal along the west side of the Kaibab arch


because, logically, that drainage would have preferably followed theproto-Kanab Creek paleocanyon already incised there (but with flowin the opposite direction). The Canaan Peak-type gravels found alongthewest side of the Kaibab arch at a present-day elevation of b2300m(b7600 ft) attest to a southward drainage having passed along thisroute sometime after a drainage reversal. In Fig. 10, this drainage isshown as having deposited these west Kaibab (WK) Canaan Peak-typegravels and then as having flowed south to converge with an UpperGranite Gorge paleocanyon at Mile 130.

Where this drainage ultimately was directed is not known, but itwas most likely not toward the west because at 25–17 Ma the areawest of Grand Canyon was still topographically high (Faulds et al.,2001). Perhaps this water was ponded in a lake. Or, if the age of LakeLong Point is extended into the late Eocene to Oligocene as proposedby Cather et al. (2008), it is even possible that an Oligocene-age,reversed-drainage system flowed southward into this still-existentlake (Fig. 10, green dotted line). If a proto-Grand Canyon had inciseddown to about Kaibab level in the vicinity of Kanab Point (Miles 130–145), then a plateau lake south of this point and perched on a KaibabLimestone surface would be reasonable. Lake Long Point is envisionedas being a shallow, widespread lake contained within a basin on theCoconino Plateau and fed by the Mogollon Highlands to the south andwest, the Kaibab arch to the east, and the emerging high plateaus ofUtah to the north.

Fig. 10. The evolution of Grand Canyon from the time of a drainage reversal (∼35 Ma?arrows=direction of water flow. Orange-balled arrows=direction of headward erosion. Gresoutheastward from the Bryce Canyon area. Blue open arrows=direction along which southwKaibab arch (WK), to its intermediate position along Johnson Creek/Cedar Knoll–Littlarrow=hypothetical drainage route down a south-dipping Supai monocline and into a still-eLimestone was progressively reduced in size by erosion. Yellow areas=remnant Canaan Pegravels east of the Kaibab arch are shown in Fig. 3). The Shivwits scarp is shown cutting aeastward to Grassy Mountain. C=Confluence, EK=East Kaibab arch, WK=West KaibabGV=Grandview monocline, CJ=Crazy Jug monocline, S=Supai monocline, PS=Peach Springs

6.1.2. Basin and Range faultingBasin and Range activity along the GrandWash fault started at 16–

17 Ma (Faulds et al., 2001), which was also a time of uplift of theColorado Plateau (Libarkin and Chase, 2003; Karlstrom et al., 2007).The Shivwits scarp had retreated northward from its Laramide HinduCanyon position (Young, 1985; Fig. 5), until it was just north of whereLower Granite Gorge is today (Fig. 10). Young (2008) proposed that acanyon—which he called a “Colorado precursor canyon”—had cutheadward (eastward) from the Grand Wash Cliffs after Basin andRange downfaulting began, had followed along this Shiwvits scarp,and then had extended eastward all the way to the Kaibab arch. Theorange-balled arrows in Fig. 10 show the section of Young's (2008)headward erosion along the Shivwits scarp; in addition, they show thedirection of regional headward erosion along our Laramide proto-Grand Canyon from Peach Springs Canyon to the Kaibab arch in thetime frame of 16–6 Ma. The 16–6 Ma headward erosion of thisprecursor canyon can, in combination with the erosion of a Laramideproto-Grand Canyon, answer the challenge posed by Spencer andPearthree (2001) of how headward erosion could have extended as faras the Kaibab arch in such a short time (∼10 Ma). It also agrees withPederson et al. (2002) and Karlstrom et al. (2007) that Quaternaryincision rates are inadequate to explain the carving of the entire GrandCanyon, and it helps explain the “missing mass” problem identified bythese authors.

) to the time of an integrated Colorado River through the canyon at ∼6 Ma. Blacken dashed arrows=direction of transport of Canaan Peak-type gravels southward andard drainage “slid” westward from its original high position along the west side of the

e Cedar Knoll/Goosenecks, to its final position along Kanab Creek. Dotted greenxistent Oligocene Lake Long Point. After this time the lake dried up and the Long Pointak-type gravels still present today along both sides of the Kaibab arch (other remnantcross the Gold Butte area, with the northernmost part of the block supplying materialarch, JC=Johnson Creek, LCK=Little Cedar Knoll, CK=Cedar Knoll, GN=Goosenecks,.


Basin and Range faulting also affected south-flowing drainagealong the west side of the Kaibab arch (Fig. 10). With the lowering ofterrain along the west-side-down Muav fault, the position of drainagein the Kanab Creek area progressively shifted toward the west fromnear the flank of the Kaibab arch to lower routes (blue arrows, Fig. 10).This shift first left behind Canaan Peak-type gravels at Johnson Creek(JC), Cedar Knoll (CK)-Little Cedar Knoll (LCK), and the Goosenecks(GN). Then, even later with west-side-down movement along theGunsight–Kanab fault, the position of south-flowing drainage “slid”farther west to its present position along Kanab Creek. This may bewhy modern Kanab Creek has only “normal,” acute, southward-directed tributaries (such as Hack and Jumpup Canyons) flowing intoit rather than barbed tributaries (Fig. 11). North-flowing drainagenever occupied this modern route because Kanab Creek formed after adrainage reversal.

Headward erosion following a Laramide paleocanyon proceededup Upper Granite Gorge until it cut into the west side of the Kaibabarch along the synclinal axis of the Grandview monocline (Fig. 10).Flowers et al. (2008) have Upper Granite Gorge incised down to aboutMississippian level by 16 Ma (Fig. 8). Hill et al. (2008) have headwarderosion eastward from Upper Granite Gorge and along the Grandviewmonocline, incising into the Kaibab arch and Redwall Limestoneaquifer by ∼6 Ma, thus effecting a karst-aquifer hydrologicalconnection between the eastern and western Grand Canyon. Head-ward erosion up Marble Canyon to Hill et al.'s (2005, 2008) “GlenLake” produced the “final connection” and the complete integration ofthe Colorado River from Colorado to the Gulf of California along aGrand Canyon similar to what exists today.

Fig. 11. The evolution of Grand Canyon from the time of a karst connection to the present (∼proto-Grand Canyon through its central section from about Miles 90 to 225 (Fig. 1). RD=secposition to its present position is proposed to have occurred. Black arrows=direction thatOrange-balled arrows=areas of headward erosion with headward erosion up Marble CanyonJug monocline, S=Supai monocline, PS=Peach Springs.

6.1.3. Headward erosion from the Grand Wash CliffsAn important question that must be addressed with regard to

headward erosion from the GrandWash Cliffs to the Kaibab arch in thetime frame of ∼16–6 Ma is: Where is all of the clastic sedimentsupposedly eroded by this drainage? Offhand, there doesn't appear tobe enough sediment in the Muddy Creek Formation at the mouth ofGrand Canyon to account for a major canyon being the supplier of thissediment. Our answer to this dilemna is: it is contained in the MuddyCreek siliciclastic and Hualapai limestone facies, but in less-volumi-nous amounts than might be expected. This is because a 16–6 Maheadward eroding canyon would have followed an already-incisedLaramide proto-Grand Canyon.

The Muddy Creek Formation is a widespread unit along the westside of the Colorado Plateau near the mouth of Grand Canyon andnorth of it. Pederson (2008) studied the Muddy Creek north of GrandCanyon and concluded that these sediments did not representterminal deposits from an ancestral Colorado River—the sameconclusion as deduced by Hill et al. (2008) based on Canaan Peak-type gravel distribution north of the canyon. In the southern GrandWash fault area, near the mouth of Grand Canyon, the Muddy CreekFormation consists of three members that grade into and interfingerwith each other:

(i) A 250-m-thick granitic fanglomerate and megabreccia facies,which is essentially an alluvial fan complex that formed in theGrand Wash trough west of the Grand Wash Cliffs and east ofWheeler Ridge as these cliffs were being uplifted along theGrand Wash fault complex (Lucchitta, 1987). The age of the

6–0 Ma). The course of the Colorado River today follows the route of the old Laramidetions of the canyon where reversal of drainage from its Laramide proto-Grand Canyonthe Colorado River, Little Colorado River, Kanab Creek, and Cataract Creek take today.breaching Glen Lake by ∼5.5 Ma. C=Confluence, GV=Grandview monocline, CJ=Crazy


fanglomerate facies was bracketed by Faulds et al. (2001)between ∼16.5 and 12 Ma, the maximum age of which recordsthe beginning of movement along the Grand Wash fault.

(i) ii) A 120-m-thick sandstone–siltstone–gypsum facies, which isa red to brown to yellow, thin-bedded unit that containsinterbedded, fine-grained clastics (sand, silt, clay) and evapor-ites (gypsum, anhydrite, halite). Faulds et al. (2001) estimatedthat this unit was somewhere between ∼13 and 11 Ma andperhaps in its uppermost part even as young as 9Ma, which agedenotes the end of major movement along the Grand Washfault. The color, texture, and composition of this facies suggestat least a partial provenance from the Hermit and SupaiFormations, while the presence of evaporites suggests a partialsource from the Kaibab, Toroweap, and Supai Formations(Wallace, 1999).

(ii) A 300-m-thick Hualapai Limestone facies consisting primarilyof impure micritic carbonate containing variable amounts ofsilt-sized detrital grains of quartz, chert, and feldspar (Fauldset al., 1997). Noncarbonate grains can constitute up to 20% ofthe carbonate-rich rocks, and the unit also contains a number ofsandstone/siltstone interbeds. The Hualapai is a freshwaterlimestone based on 87Sr/86Sr ratios (Patchett and Spencer,2001) and δ13C–δ18O values (Faulds et al., 1997), with thewestern Grand Canyon themost likely source of the large influxof freshwater into the Grand Wash trough (Wallace, 1999). Theage of the Hualapai Limestone was bracketed by Faulds et al.(2001) between ∼11 and 6 Ma.

Now, consider a canyon headward-eroding from the Grand WashCliffs just south of the Shivwits scarp in the time frame of 16–6 Ma, asproposed by Young (2008). This precursor canyon would have beguncutting into the Paleozoic section of the Colorado Plateau as the Basinand Range down-dropped. While Mississippian to Cambrian rock wasbeing carved on the Hualapai Plateau side of the scarp (Young, 1985;Beard, 1996; Young, 2008), the Kaibab, Toroweap, Coconino, Hermit,and Supai Formations were still in existence and being eroded alongthe north side of the scarp, thus supplying red sand, silt, andevaporites to the sandstone–siltstone–gypsum facies of the MuddyCreek Formation at the mouth of the forming canyon.

As headward erosion progressed eastward beneath the Shivwitssection of the western Grand Canyon, it would have breached theRedwall–Muav aquifer causing carbonate-rich groundwater to emergeas spring water that ultimately flowed westward into the Hualapaiinterior basin. This explains the similarity of 87Sr/86Sr values of theHualapai Limestonewith speleothems deposited from Redwall aquiferwater (Hill et al., 2008; Polyak et al., 2008). We propose that thebeginning of major spring sapping began in Young's (2008) precursorcanyon ∼11 Ma—the age of the oldest limestone unit in the HualapaiLimestone.

A canyon headward-eroding eastward from the Grand Wash Cliffswould have intersected a pre-existent Laramide proto-Grand Canyonin the vicinity of Diamond Creek (Fig. 5); from there, further headwarderosion up this paleochannel to the north and then east would havecommenced. Erosion of upper Paleozoic clastic units (Toroweap,Coconino, Supai) along this paleocanyon would have been minimalbecause these units had already been incised by a proto-Grand Canyonearlier in time; hence, very little clastic sediment would have beensupplied to the Muddy Creek Formation. Young (2008) proposed thatthe drainage area of a hydrologic basin containing a 16–6 Maheadward-eroding river would have included the Hualapai Plateauand the combined ancestral drainages of Kanab and Cataract Creekson the west side of the Kaibab arch—or an approximate 13,000 km2

hydrologic basin that would have had nomore than 1–2% of the runoffassociated with the modern (pre-dam) Colorado River discharge.Flowers et al. (2008) have the Upper Granite Gorge section of thecanyon incised to about Mississippian level by 16 Ma (Fig. 8), so after

the time of a precursor canyon/proto-Grand Canyon connection,incision of the Redwall–Muav aquifer in the Upper Granite Gorge areawould have continued to supply carbonate-rich water to the HualapaiLimestone until ∼6 Ma, at which time the Colorado River becameintegrated through Grand Canyon. Some clastic material would havebeen supplied to this westward-flowing river system via tributariescutting into upper Paleozoic clastic units, and these clastics arerepresented by detritus in the Hualapai Limestone.

6.2. 6–0 Ma

After a karst connection between the eastern and western GrandCanyon occurred at∼6Ma and a final connection at∼5.5Ma (Hill et al.,2008), an integrated Colorado River cut Grand Canyon to the depth it istoday. Thismajor period of erosion, plus the headward erosion of a 16–6 Ma precursor canyon, agrees with Flowers et al.'s (2008) youngesthelium dates from Upper Granite Gorge that constrain substantialincision of themodernGrandCanyon below theKaibab surface to post-23 Ma. After an ∼6Ma eastern-western Grand Canyon connection, theancestral Little Colorado River became segmented into two sections: areversed-drainage Marble Canyon section flowing south and a LittleColorado River Canyon section flowing north to connect with theColorado River at the Confluence (Figs.1 and 11). Headward erosion upthese two canyons produced the geomorphology that is seen today,with the Little Colorado River cutting into the 16–6 Ma BidahochiFormation (Dallegge et al., 2001). Further incision up Cataract Creekalso cut into and eroded the northern portion of the Long PointLimestone on the Coconino Plateau. In Fig.11, the symbol RD stands forthe sections of Grand Canyon drainage that are proposed to havereversed from the position of a Laramide proto-Grand Canyon andancestral Little Colorado River (Fig. 5).

7. Conclusion

The basic premise of this proposed proto-Grand Canyon model isthat the modern Colorado River utilized elements of Laramidepaleotopography to establish its course across the central GrandCanyon. The configuration of Grand Canyon today is thus dependenton this original paleocanyon route, with later sections of canyonintegrating with it to produce the drainage pattern seen today. Thepresent-day route of the Colorado River through the central GrandCanyon is not exactly the same as it was in the Laramide: Basin andRange-age faulting and other factors have modified this coursesomewhat. But the present route of the Colorado River throughGrand Canyon is confined within the boundaries set by a Laramideproto-Grand Canyon and by later segments that became connected tothis paleocanyon.

Acknowledgements

This study is part of a larger project supported by the NationalScience Foundation to determine the age of Grand Canyon by thedating of speleothems in Grand Canyon caves. Grants from theNational Park Service, Grand Canyon Association, and NationalSpeleological Society supported field work for this project. Theauthors especially thank the other members of our gravel group,Bob Scarborough and Doug Powell, for field support. We also thankDick Holm for field support and for help with petrologic identificationof gravel clasts and George Billingsley for supplying directions togravel localities. Strontium analyses were done by Victor Polyak at theUniversity of New Mexico Geochronology Lab. We thank EmmaBenenati and John Rihs of Grand Canyon National Park, Doug Powelland Mike Salamacha of Grand Staircase-Escalante National Monu-ment, and Kyle Voyles of Grand Canyon-Parashant National Monu-ment for administrative support of this project. Finally, we thank fourthoughtful reviewers who improved the manuscript.


References

Beard, L.S., 1996. Paleogeography of the Horse Spring Formation in Relation to the LakeMead Fault System, Virgin Mountains, Nevada and Arizona. Special Paper, vol. 303.Geological Society of America, Boulder, CO, pp. 27–60.

Billingsley, G.H., 1992. Geologic Map of the Jumpup Canyon and Big SpringsQuadrangles, Mohave and Coconino Counties, Arizona. U.S. Geological SurveyMiscellaneous Investigations Map I-2290. Scale 1:62,500. Denver, CO.

Breed, W.J., 1969. A Pliocene river channel in Wupatki National Monument, Arizona.Journal Arizona Academy Science 5, 177–181.

Cather, S.M., Connell, S.D., Chamberlin, R.M., McIntosh, W.C., Jones, G.E., Potochnik, A.R.,Lucas, S.G., Johnson, P.S., 2008. The Chuska erg: paleogeomorphic and paleoclimaticimplications of an Oligocene sand sea on the Colorado Plateau. Geological Society ofAmerica Bulletin 120 (1/2), 13–33.

Dallegge, T.A., Ort, M.H., McIntosh, W.C., Perkins, M.E., 2001. Age and depositionalbasin morphology of the Bidahochi Formation and implications for the ancestralupper Colorado River. In: Young, R.A., Spamer, E.E. (Eds.), Colorado River: Originand Evolution. Monograph, vol. 12. Grand Canyon Association, Grand Canyon, AZ,pp. 47–51.

Dutton, C.E., 1882. Tertiary History of the Grand Canyon District. Monograph, vol. 2. U.S.Geological Society, Washington, DC. 264 pp.

Eaton, J.G., Hutchinson, J.H.,1995. A late Eocene fauna from undescribed strata overlyingthe Claron Formation, Sevier Plateau, southwestern Utah. Geological Society ofAmerica Abstracts with Programs 27, 10.

Ehlers, T.A., Farley, K.A., 2003. Apatite (U–Th)/He thermochronometry: methods andapplications to problems in tectonic and surface processes. Earth and PlanetaryScience Letters 206, 1–14.

Elston, D.P., Young, R.A., 1991. Cretaceous–Eocene (Laramide) landscape developmentand Oligocene–Pliocene drainage reorganization of transition zone and ColoradoPlateau, Arizona. Journal Geophysical Research 96 (B7), 12389–12406.

Faulds, J.E., Schreiber, B.C., Reynolds, S.J., González, L.A., Okaya, D., 1997. Origin andpaleogeography of an immense nonmarine Miocene salt deposit in the Basin andRange (western USA). Journal of Geology 105, 19–36.

Faulds, J.E., Price, L.M., Wallace, M.A., 2001. Pre-Colorado River paleogeography andextension along the Colorado Plateau–Basin and Range boundary, northwesternArizona. In: Young, R.A., Spamer, E.E. (Eds.), Colorado River: Origin and Evolution.Monograph, vol. 12. Grand Canyon Association, Grand Canyon, AZ, pp. 93–99.

Flowers, R.M., Wernicke, B.P., Farley, K.A., 2007. (U–Th)/He apatite constraints on theerosional history of the southwestern Colorado Plateau and implications for EarlyTertiary uplift and carving of a “proto-Grand Canyon”. Geochimica et CosmochimicaActa 71 (15), A287 (abstract).

Flowers, R.M., Wernicke, B.P., Farley, K.A., 2008. Unroofing, incision, and uplift history ofthe southwestern Colorado Plateau from apatite (U–Th)/He thermochronometry.Geological Society of America Bulletin 120, 571–587.

Ford, D.C., Williams, P.W., 1989. Karst Geomorphology and Hydrology. Unwin Hyman,London. 601 pp.

Gierlowski-Kordesch, E.H., Jacobson, A.D., Blum, J.D., Garces, B.L., 2008. Watershedreconstruction of a Paleocene–Eocene lake basin using Sr isotopes in carbonaterocks. Geological Society of America Bulletin 120, 85–95.

Goldstrand, P.M., 1990. Stratigraphy and Paleogeography of Late Cretaceous andPaleogene Rocks of Southwest Utah. Utah Geological and Mineral SurveyMiscellaneous Publication, Salt Lake City, UT, 58 pp.

Goldstrand, P.M., 1994. Tectonic development of Upper Cretaceous to Eocene strata ofsouthwestern Utah. Geological Society of America Bulletin 106, 145–154.

Goldstrand, P.M., Eaton, J.G., 2001. Paleocene to Early Oligocene paleogeography,southwestern Utah. In: Young, R.A., Spamer, E.E. (Eds.), Colorado River: Originand Evolution. Monograph, vol. 12. Grand Canyon Association, Grand Canyon, AZ,pp. 25–29.

Hill, C.A., Ranney, W.D., 2007. A proposed Laramide proto-Grand Canyon. GeologicalSociety of America Abstracts with Programs 39 (5), 43 Rocky Mountain section.

Hill, C.A., Ranney, W.D., Scarborough, R.B., Powell, J.D., 2005. Search for the ancestralColorado River. Geological Society of America Abstracts with Programs 37 (6), 36Rocky Mountain section.

Hill, C.A., Eberz, N., Buecher, R.H., 2008. A karst connection model for Grand Canyon,Arizona, USA. Geomorphology 95 (3–4), 316–334.

Hill, C.A., Scarborough, R.B., Powell, J.D., Ranney, W.D., 2006. Report on gravelobservations along the Escalante River, on the Marble Platform, Echo Cliffs, HouseRock Valley, Kanab Point, and in Wupatki National Monument. Unpublished reportin the files of the Geology Department, Northern Arizona University, Flagstaff, AZ,35 pp.

Holm, R.F., 2001. Cenozoic paleogeography of the central Mogollon Rim, southernColorado Plateau region, Arizona, revealed by Tertiary gravel deposits, Oligocene toPleistocene lava flows, and incised streams. Geological Society of America Bulletin13 (11), 1467–1485.

Hunt, C.B., 1956. Cenozoic Geology of the Colorado Plateau. Professional Paper, vol. 279.U.S. Geological Survey, Washington, DC. 99 pp.

Hunt, C.B., 1969. Geologic History of the Colorado River: The Colorado River Region andJohn Wesley Powell. Professional Paper, vol. 669-C. U.S. Geological Survey,Washington, DC, pp. 59–230.

Huntoon, P.W., 1995. Is it appropriate to apply porous media groundwater circulationmodels to karstic aquifers? In: El-Kadi, A.I. (Ed.), Groundwater Models for ResourceAnalysis and Management. CRC Lewis Publishers, Boca Raton, FL, pp. 339–358.

Huntoon, P.W., 2000. Variability in karstic permeability between unconfined andconfined aquifers, Grand Canyon region, Arizona. Environmental and EngineeringGeoscience 6 (2), 155–170.

Huntoon, P.W., Billingsley, G.H., Sears, J.W., Ilg, B.R., Karlstrom, K.E., Williams, M.L.,Hawkins, D., 1996. Geologic map of the Eastern Grand Canyon National Park,Arizona. scale 1:62,500, Grand Canyon Association, Grand Canyon, AZ.

Karlstrom, K.E., Crow, R.S., Peters, L., McIntosch, W., Raucci, J., Crossey, L.J., Umhoefer, P.,Dunbar, N., 2007. 40Ar/39Ar and field studies of Quaternary basalts in Grand Canyonand model for carving Grand Canyon: quantifying the interaction of river incisionand normal faulting across the western edge of the Colorado Plateau. GeologicalSociety of America Bulletin 119 (11/12), 1283–1312.

Koons, E.D., 1964. Structure of the eastern Hualapai Indian Reservation, Arizona. ArizonaGeological Society Digest 7, 97–114.

Lamb, M., Umhoefer, P.J., Anderson, E., Beard, L.S., Hickson, T., Martin, K.L., 2005.Development of Miocene faults and basins in the Lake Mead region. In:Pederson, J.L., Dehler, C.M. (Eds.), Interior Western United States. Field Guide,vol. 6. Geological Society of America, Boulder, CO, pp. 389–418.

Libarkin, J.C., Chase, C.G., 2003. Timing of Colorado Plateau uplift: initial constraintsfrom vesicular basalt-derived paleoelevations: comment and reply. Geology 31 (2),191–192.

Lucchitta, I., 1975. The Shivwits Plateau. In: Goetz, A.F., Billingsley, F.C., Gillespie, A.R.,Abrams, M.J., Squires, R.L. (Eds.), Application of ERTS Images and Image Processingto Regional Geologic Problems and Geologic Mapping in Northern Arizona. NASA-JPL Technical Report 32-1597, Pasadena, CA, pp. 41–73.

Lucchitta, I., 1987. The Mouth of the Grand Canyon and Edge of the Colorado Plateau inthe Upper Lake Mead Area, Arizona. Geological Society of America Centennial FieldGuide. Rocky Mountain section, Boulder, CO, pp. 365–370.

Lucchitta, I., McKee, E.H., 1975. New geochronologic constraints on the history of theColorado River and the Grand Canyon. Geological Society of America Abstracts withPrograms 7 (3), 342.

Lucchitta, I., Jeanne, R.A., 2001. Geomorphic features and processes of the ShivwitsPlateau, Arizona, and their constraints on the age of western Grand Canyon. In:Young, R.A., Spamer, E.E. (Eds.), Colorado River: Origin and Evolution. Monograph,vol. 12. Grand Canyon Association, Grand Canyon, AZ, pp. 65–69.

Monroe, S.A., Antweiler, R.C., Hart, R.J., Taylor, H.E., Truini, M., Rihs, J.R., Felger, T.J., 2005.Chemical Characteristics of Ground-water Discharge Along the South Rim of GrandCanyon in Grand Canyon National Park, Arizona, 2000–2001. U.S. Geological SurveyScientific Investigations Report 2004-5146, Denver, CO. 59 pp.

Patchett, P.J., Spencer, J.E., 2001. Application of Sr isotopes to the hydrology of the ColoradoRiver system waters and potentially related Neogene sedimentary formations. In:Young, R.A., Spamer, E.E. (Eds.), Colorado River: Origin and Evolution. Monograph, vol.12. Grand Canyon Association, Grand Canyon, AZ, pp. 167–171.

Pederson, J., 2008. The mystery of the pre-Grand Canyon River: results from the MuddyCreek Formation. GSA Today 18 (3), 4–10.

Pederson, J., Karlstrom, K., Sharp, W., McIntosh, W., 2002. Differential incision of theGrand Canyon related to Quaternary faulting—constraints from U-series and Ar/Ardating. Geology 30 (8), 739–742.

Polyak, P., Hill, C., Asmeron, Y., 2008. Age and evolution of Grand Canyon revealed by U–Pb dating of water-table-type speleothems. Science 319, 1377–1380.

Powell, J.W., 1875. Exploration of the Colorado River of the West and its tributaries: Onthe Physical Features of the Valley of the Colorado. Smithsonian Institution,Washington DC, pp. 149–214.

Ranney, W.D., 1998. Geomorphic evidence for the evolution of the Colorado River in theLittle Colorado-Marble Canyon area, Grand Canyon, Arizona. Geological Society ofAmerica Abstracts with Programs 30 (6), 34.

Ranney, W.D., 2005. Carving Grand Canyon. Grand Canyon Association, Grand Canyon,AZ. 160 pp.

Reches, Z., 1978. Development of Monoclines: Part 1. Structure of the Palisades CreekBranch of the East Kaibab monocline, Grand Canyon, Arizona. Memoir, vol. 151.Geological Society of America, Boulder, CO, pp. 235–271.

Roller, J.A., 1989. Fracture history of the Redwall Limestone, Lower Supai Group andTertiary Units on the Hualapai Indian Reservation, Northwestern Arizona:additional data to open-file peport 87-359. U.S. Geological Survey Open File Report89-463, Boulder, CO. 49 pp.

Scarborough, R.B., Hill, C.A., Ranney, W.D., Powell, J.D., 2007. Report on gravelobservations at Grassy Mountain andMt. Trumbell, Parashant National Monument;east and west sides of Kaibab arch, Kaibab National Forest; Shoshone Point andDesert View areas, Grand Canyon National Park; and Long Point, private and Stateland. Unpublished report in the files of the Geology Department, Northern ArizonaUniversity, Flagstaff, AZ, 35 pp.

Spencer, J.E., Pearthree, P.A., 2001. Headward erosion versus closed-basin spillover asalternative causes of Neogene capture of the ancestral Colorado River by the Gulf ofCaliforna. In: Young, R.A., Spamer, E.E. (Eds.), Colorado River: Origin and Evolution.Monograph, vol. 12. Grand Canyon Association, Grand Canyon, AZ, pp. 215–219.

Wallace, M.A., 1999. Cenozoic stratigraphic and structural framework of the southernGrand Wash trough, northwestern Arizona: paleographic implications. Unpub-lished M.S. thesis, University of Iowa, Iowa City, 119 pp.

Wenrich, K.J., Billingsley, G.H., Huntoon, P.W., 1997. Breccia-pipe and Geologic Map ofthe Northeastern Part of the Hualapai Indian Reservation and Vicinity, Arizona. U.S.Geological Survey Map I-2440, vol. 1:48,000, Denver, CO.

Young, R.A., 1982. Paleomorphic evidence for the structural history of the ColoradoPlateau margin in western Arizona. In: Frost, E.G., Martin, D.L. (Eds.), Mesozoic–Cenozoic Tectonic Evolution of the Colorado Region, California, Arizona, andNevada. Cordilleran Publishers, San Diego, CA, pp. 29–39.

Young, R.A., 1985. Geomorphic evolution of the Colorado Plateaumargin inwest-centralArizona: a tectonic model to distinguish between the causes of a rapid symmetricalscarp retreat and scarp dissection. In: Morisawa, M., Hack, J.T. (Eds.), TectonicGeomorphology. Proceedings 15th Ann. Binghamton Geomorphology Symposium.Allen and Unwin, Boston, MA, pp. 261–278.


Young, R.A., 1987. Landscape development during the Tertiary. In: Graf, W.L. (Ed.),Geomorphic Systems of North America. Centennial Special, vol. 2. GeologicalSociety of America, Boulder, CO, pp. 265–302.

Young, R.A., 2001. The Laramide Paleogene history of the western Grand Canyonregion: setting the stage. In: Young, R.A., Spamer, E.E. (Eds.), Colorado River:Origin and Evolution. Monograph, vol. 12. Grand Canyon Association, GrandCanyon, AZ, pp. 7–15.

Young, R.A., 2008. Pre-Colorado River drainage in western Grand Canyon: potentialinfluence onMiocene stratigraphy in GrandWash trough. In: Reheis, M.C., Hershler,R., Miller, D.M. (Eds.), Late Cenozoic Drainage History of the Southwestern Great

Basin and Lower Colorado Region: Geologic and Biotic Perspective. GeologicalSociety of America Special Paper 439, Ch. 14, 319–334.

Young, R.A., Brennan, W.J., 1974. Peach Springs Tuff: its bearing on structural evolutionof the Colorado Plateau and development of Cenozoic drainage in Mohave County,Arizona. Geological Society of America Bulletin 85, 83–90.

Young, R.A., McKee, E.H., 1978. Early andmiddle Cenozoic drainage and erosion inwest-central Arizona. Geological Society of America Bulletin 89, 1745–1750.

A Proposed Laramide Grand Canyon

Documents

Transcript of A Proposed Laramide Grand Canyon