Paleogene Grand Canyon Incompatible with Tertiary Paleogeography and Stratigraphy

CRevolution 2: Origin and Evolution of the Colorado River System II themed issue

Paleogene Grand Canyon incompatible with Tertiary paleogeography and stratigraphy

Richard A. Young1 and Ryan Crow2 1Department of Geological Sciences, State University of New York, 1 College Circle, Geneseo, New York 14454, USA 2Department of Earth & Planetary Sciences, University of New Mexico, MSC03-2040, Albuquerque, New Mexico 87131, USA

ABSTRACT Paleogene ancestral precursor to the modern the accompanying evolutionary changes in the Colorado River gorge. Instead, all the fi eld Hualapai Plateau drainage system that clearly The Hualapai Plateau in northwest Ari- evidence clearly supports a late Miocene– preceded the modern Grand Canyon. zona, the location of the western Grand Can- Pliocene origin for integration of the western yon, contains an unusually lengthy Tertiary Grand Canyon on the central Hualapai Pla- Condensed Tertiary History stratigraphic record dominated by fl uvial teau with the upper Colorado River. deposition and extending from at least late The Hualapai Plateau in northwestern Ari- Paleocene through late Miocene time. The INTRODUCTION zona contains one of the most complete geo- thickest and oldest Tertiary sections are best logic records of Tertiary events on the Colorado exposed in a system of partially re-exhumed Grand Canyon Controversy Plateau from Paleocene through Miocene time. Laramide paleocanyons. The Paleogene This brief review is condensed from Young drainage system was locally disrupted and The western Grand Canyon on the Hualapai (1966, 1999, 1982, 2001a, 2001b) and is best ponded by Laramide monoclines. In pre- Plateau (Fig. 1) has recently become the focus understood by viewing geologic maps of the Oligocene time, extensive alluvial fans spread of apatite U-Th/He and fi ssion-track studies area by Young (1966, 2011), by Billingsley southward from the Shivwits Plateau scarp by researchers debating the evidence for and et al. (1999, 2000), and by Wenrich et al. (1996). across the current location of the modern against the possible existence of an ancestral Laramide events recorded on the Hualapai Pla- Colorado River gorge to the northern mar- Grand Canyon in the same location and nearly teau began with the uplift and stripping of the gin of the Laramide drainage system at as deep as the modern Colorado River gorge as Upper Paleozoic sedimentary rocks to form a Hindu Canyon. Locally derived, fl uvial Buck early as 70 Ma (Flowers and Farley, 2012, 2013; cuesta-scarp landscape into which canyons were and Doe Conglomerate subsequently fi lled Wernicke, 2011; Karlstrom et al., 2013, 2014). contemporaneously incised (Figs. 1 and 2). The the disrupted Paleogene channels, spilled However, stratigraphic and geomorphologic term Laramide in this discussion includes the out over the local interfl uves, and formed an fi eld evidence directly confl icts with the exis- events from ca. 85 Ma to 40 Ma (Campanian extensive aggradational surface of low relief tence of a deep Paleogene canyon coinciding to mid-Eocene) in Arizona as described by by late Oligocene time. Early Miocene vol- with the location of the modern Colorado River Keith and Wilt (1985), and by the correspond- canism fi lled in much of the relict Laramide gorge, although an argument has been made ing radiometric age distribution compiled by relief. Erosional recession of the adjacent that headward erosion from the west could have Damon (1964). The major Laramide paleocan- Shivwits Plateau escarpment shifted the begun gradually to establish the modern canyon’s yon segments include the L-shaped Milkweed- northern Hualapai Plateau margin 8 km course in middle to late Miocene time (Young, Hindu channel on the central Hualapai Plateau northeastward after the Laramide drainage 2008), slightly earlier than the conventionally and Peach Springs Canyon, the trunk valley episode and before the incision by the mod- accepted time for integration of the Colorado coincident with the Hurricane fault (Young, ern Colorado River. Partially exhumed trib- River at 6–5 Ma. The strongest evidence against 1966, 1979, 1982, 2001a). The paleocanyons utaries to the Hindu Canyon paleochannel a Paleogene ancestral Grand Canyon includes: preserve the greatest buried relief at the plateau and associated sedimentary deposits border- (1) a nearly continuous stratigraphic record margin, 1200 m near Truxton, Arizona, and ing the southern edge of the Grand Canyon documenting a lengthy episode of Paleocene become shallower downstream to the northeast. gorge demonstrate that local surface runoff through Miocene deposition throughout the The oldest fl uvial deposit that records the fl owed south, away from the modern Grand Hualapai Plateau, and (2) fanglomerate deposits nature and existence of the northeast-fl owing Canyon location, during early Paleogene of Paleocene–Eocene age preserved along the Laramide drainage system and fi lls the low- time. Headwardly eroding Colorado River south rim of the Grand Canyon that contain est portions of these abandoned canyons is the tributaries exhumed, captured, and reversed distinctive sedimentary clasts derived from the Music Mountain Formation, a correlative of the the fl ow of these tributaries to the Laramide younger Paleozoic rocks capping the Shivwits so-called “Rim gravel” of the Mogollon Rim canyon, beginning in late Miocene or Plio- Plateau escarpment on the opposite side of the region in central Arizona (Cooley and David- cene time. The geomorphic and stratigraphic canyon (Fig. 2). This paper focuses on the Ter- son, 1963; Young, 1999). The age of the regional records show no evidence of, and provide tiary events most closely associated with the base of these extensive gravels is uncertain but no space for, incision of a Late Cretaceous– Laramide-Paleogene stratigraphic record and may range back to an early or intermediate

Geosphere; August 2014; v. 10; no. 4; p. 664–679; doi:10.1130/GES00973.1; 13 ﬁ gures; 1 table. Received 31 July 2013 ♦ Revision received 18 April 2014 ♦ Accepted 28 May 2014 ♦ Published online 24 June 2014

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Paleogene Grand Canyon unlikely N River 15 km

Mogollon Navajo Bridge Highlands Figure 1 Colorado

LOCATION MAP LOCATION Platform ARIZONA Little Flagstaff

San Francisco Field Volcanic Marble Lees Ferry ediately next to its junction with Glen Canyon Dam

Springs Wash on some published maps. Wash Springs

state 40

n I (Topography Omitted Here) Sycamore Canyon graphic detail. Abbreviations: PS—Peach Springs, Abbreviations: graphic detail. Grand Canyon Village (2750 m) Kaibab Upwarp Bill Williams Mt. Volcanics Williams (1710 m) Plateau Coconino Ashfork Tank Creek Duff Brown Duff Cataract Point Kanab Creek

Long

I I

I I I

I I

I I I I I I I I I I I

Black Tank

I I

I Tank

Furguson I I

Subcrop I Supai Road Supai Mt Floyd Volcanics

I Limestone

I Long Point

I I I I I I I I I I I I I I

I I

IIII

I Seligman (1750 m) I

I I

Plateau I

I I I

I I

I I I

I I I I I I I I I

I I I I I I I I I I I I I I I I I I

Kanab

I I I I

I I

Colorado River Colorado I

I I I I

I I I

faul p I

e I I I I I w

I I I I I

o I I I I I I

Wells r

I I I I I o I I

I I T I I

I I I I I I

I I I I Frazier I I I I I I

I I I I

I I

I I I I

DU I I

I I I

I I I I I I

I I I I I I I I I I I I I

I I

I I I I I I I I t 66

I I

I I II I I I I I I I R

I I I

I I

I 40 Interstate I I

I I I I I I

out Ck. out

I I I

I I I I I I I I I r I I I I I I

lt I I

u I I I T

a I I I DU I I I I f I I I I I I I I I I

ane I Hurric I

I I I I I I I Blue Mt.

III I I

I I

I I I

I I I I I I

I I

I I I

I (Original Music Mt.)

I I I

I I

I Mohon Mountains

I Point

I I

I I I I

I I I I I Caldera Cherokee I l I I K I I

e I I I I

I n I I Sp. C. Sp. I I I I I I I I I I n I I I I I I PS I I I a I I Aquarius Mountains

I I I

I I I I I h I Peach I

I I I I

I I C I Valley

I I I I I I I I I

I I

I I I I I I u I I

I I I Canyon I I

I I I II

I I BC d I I I I I I I

I I I I I I

I I I I I I n I I I

I I i I

Tr I I (1830 m) I

I I I I I

I I I I I I

I I

H I

I fault I

- I

I I

Plateau I

I I I d

Separation I I

I I

I I I Hurricane

I I III I I

e I

I I I I

I I I I I I

I I I

w Music

I Mts

I I I I

I I I k

Shivwits l I i I

I I I M I

I I I Truxton I I I n I I I I I I I I I I I I I I I I I I I I I I I I I o I I I I I I I I I I I I I I I I I I I I

Spencer Canyon I I y I I I I I I I I I I I I I I I I

I I I I I I I I n I

I I a I Mts.

I I I I I C ck I I I I I o I I I I I d I ac I I I I n I fs e

I I I I I I I I I P

I I I I a I lif

I I I I II r I

s I C f f

i I l I h C

I Ia I I I I G I

W I I I I I

d I I I sh

n I I I I I I a I I

r I

I (1525 m) I Wa G I o II I I I d

Key Localities I I I I I 66 Rt I I I ran

114 W I I Plateau G I I I I Hualapai I I I I I Wash I I I I I I I Grand Trough I I I I I I I I I I I I I I I I I I I I I I I I I I I I I

Southern Laramide Channels with Flow Directions NORTHWESTERN ARIZONA Red Lake (900 m) Valley Lake Mead Hualapai Limestone Hualapai Kingman o 36 N Figure 1. General location map for features and localities mentioned in text. Eastern half of map is generalized omits topo features 1. General location map for Figure Peach Springs is labeled of Peach Springs Canyon near The headward reach Peach Springs Canyon, is named Lost Man Canyon. BC—Bridge Canyon, Tr—Truxton, K—Kelly Point. The short, disconnected, eastern end of Hindu Canyon (Milkweed-Hindu channel), imm K—Kelly Point. Tr—Truxton, BC—Bridge Canyon,

Geosphere, August 2014 665

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Young and Crow

The basal Milkweed member of the Buck and Doe Conglomerate is dominated by clasts from Cambrian through Mississippian carbonates that crop out on the western Hualapai Plateau. In the Peach Springs Canyon headwaters, a younger conglomerate member deposited during the Buck and Doe episode records an inﬂ ux of more exotic clasts derived from local Precambrian basement exposures around the margins of the Truxton Val- ley (Fig. 1), a wide erosional reentrant in the pla-

F teau margin that coincides with the trend of the Hurricane fault and parallel structural trends in the Precambrian basement (Beard and Lucchitta , 1993). Although this younger, arkosic, Peach Springs member of the Buck and Doe Conglom- erate superfi cially resembles the basal Music Mountain Formation, the crystalline clasts in the younger Peach Springs member of the Buck and Doe Conglomerate are clearly derived from identifi able Precambrian outcrops currently bor- dering the Truxton Valley and are markedly less weathered (Young, 1999; Beard and Lucchitta, Figure 2. View to northwest from Kelly Point across Hualapai Plateau, along Shivwits Pla- 1993). This vertical sedimentological change teau scarp (upper right), with large tributary (F) to Separation Canyon in left foreground present in the Peach Springs member records the (F on Fig. 3). Width of canyon at F is 750 m, as also depicted on map of Fig. 3 at F. progressive headward erosion by upper Peach Springs Wash tributaries as they expanded southwestward into the Truxton Valley following the stage of the Late Cretaceous Laramide uplift. The Laramide drainage on the Hualapai Pla- demise of the Laramide drainage. Gravel lenses within the arkosic Music Moun- teau was eventually disrupted by structural defor- The two Buck and Doe Conglomerate mem- tain Formation are dominated by exotic Pre- mation along Laramide monoclines, which were bers fi lled most of the remaining paleocanyon cambrian crystalline clasts derived from the subsequently beveled by erosion prior to late topography and gradually covered the central central Arizona Mogollon highlands and the Oligocene time. Throughout the remainder of Hualapai Plateau to form a relatively uniform Kingman uplift, regional Laramide uplands bor- the Tertiary history, the basins formed by the iso- surface of low relief at elevations close to dering the plateau as described by Cooley and lated portions of the Laramide canyons became 1462 m (4800 ft). This episode of fl uvial depo- Davidson (1963), Lucchitta (1966), and Faulds closed depocenters, which have preserved a con- sition was disrupted locally by volcanism at et al. (2001). The vertical changes in gravel tinuous geologic record of events until incision the onset of the Basin and Range orogeny. The clast lithologies clearly record the progres- by modern Colorado River tributaries. At the uppermost beds of the Milkweed member of the sive unroofi ng of the adjacent source terranes time of Laramide drainage disruption and con- Buck and Doe Conglomerate on the Hualapai (Young, 2001b). current cessation of Music Mountain deposition, Plateau locally contain reworked volcanic Along the margins of the Hualapai Plateau the local bedrock relief on the Laramide chan- detritus, which heralds the onset of Basin and paleocanyons, locally derived colluvium, debris nels varied from 75 to 600 m, with average relief Range volcanism adjacent to the plateau. Basalt fl ows, and landslides, including meter-sized being greater along the Peach Springs Canyon– fl ows, as well as the widespread Peach Spring Paleozoic limestone blocks, form a crudely Truxton Valley segment (Fig. 1). Tuff, breached the topographic lows along the stratifi ed orange fanglomerate inferred to have Following ponding and formation of fresh- southern Grand Wash Cliffs, and fl owed north- formed under humid to subtropical oxidizing water limestones in localized basins on the eastward onto the plateau, although a few basalts conditions. The Hindu Fanglomerate inter- upstream sides of the monoclines within Milk- have eruptive vents located on the Huala pai Pla- fi ngers laterally with the Music Mountain For- weed and Peach Springs Canyons, the Laramide teau proper. The brief volcanic episode lasted mation along channel margins and near promi- paleochannels were completely fi lled with from ca. 19 Ma to 16 Ma. nent scarps. locally derived Buck and Doe Conglomerate. During and following Miocene volcanism, This Late Cretaceous(?)–Eocene history is The change from exotic, distantly derived clasts, fl uvial deposition of locally derived Willow similar to the geologic record preserved along to locally derived gravels suggests that undocu- Springs Formation occurred across the lower the plateau margin in southern Utah described mented Paleogene faulting might have occurred elevations throughout the Hualapai Plateau. by Goldstrand (1990, 1992). The approximate along the southern Grand Wash Cliffs to account This Miocene–Pliocene gravel locally exceeds timing of the primary episode of Laramide uplift for the exclusion of the earlier Precambrian 100 m in thickness, but it is typically less indu- and timing of the initial erosion of the south- sediment sources. The southern Grand Wash rated than similar Buck and Doe Conglomer- western Colorado Plateau are constrained as Cliffs fault scarp that forms the plateau margin ate beds. Absent basalt fl ows, the only clear occurring prior to 50 Ma by thermochronologic is more erosionally embayed and presumably distinction between these local postvolcanic data (Flowers et al., 2008). Fossil data imply much older than the linear Miocene fault bound- gravels and the underlying Buck and Doe Con- widespread erosion prior to Eocene time (Young ary nearer Lake Mead (Lucchitta, 1966; Beard glomerate Milkweed member is the inclusion of and Hartman, 2011). et al., 2007). volcanic clasts in the younger Coyote Springs

666 Geosphere, August 2014

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Paleogene Grand Canyon unlikely

Formation. In the more isolated Truxton Valley, Long Point (Young, 1982; Fig. 1). Early Eocene of the Shivwits Plateau on the north side of the post vol canic fl uvial deposition continued into or late Paleocene(?) gastropods occur in a series modern Grand Canyon (Figs. 2, 3, and 4). Pleistocene time (Twenter, 1962). The timing of thin limestone lenses at Duff Brown Tank Young (1966, 1999, 2001a, 2001b) mapped of cessation of deposition of the Coyote Springs (Fig. 1; Young and Hartman, 2011, 2014). and redefi ned eight Tertiary stratigraphic and Formation and subsequent incision by Colorado The recently located ash bed near the top of volcanic units (Fig. 5), described the Laramide River tributaries is not obvious from any evi- the Peach Springs member of the Buck and Doe step-bench or cuesta-scarp landscape of the dence observed in the youngest sediments. Conglomerate in Peach Springs Wash is 24.12 ± Hualapai Plateau, and proposed that the older 0.04 Ma, or late Oligocene (see Appendix 1). Milkweed-Hindu Canyon paleochannel was Chronologic Control The ash locality is 2.4 km northeast of the town defl ected eastward toward the Hurricane fault of Peach Springs (Young, 2011) and strengthens zone from its dip-parallel course when it encoun- The Tertiary sedimentary fi ll on the Huala- the argument for the proposed Laramide age tered the colluvial footslope of the Shivwits scarp pai Plateau has a maximum thickness of 420 m of the thick Paleogene sedimentary sequence at a preexisting Laramide position (Young, 1982, (1380 ft) in Peach Springs Wash (Young, 1999, below (Table 1; Young et al., 2011). The evi- 1985; Figs. 3 and 4). The right-angle bend in the 2011). The limited geochronologic control for the dence of widespread aggradation from late paleocanyon drainage pattern from Milkweed entire Tertiary section preserved on the Hualapai Laramide through Miocene time in locations into Hindu Canyon (Fig. 1) is logically the result Plateau is based on several gastropod species in scattered across the Hualapai Plateau would of a classic, dip-parallel, scarp-controlled drain- the Music Mountain Formation at Long Point appear to be incompatible with contemporane- age pattern developed on a cuesta-scarp land- (Young and Hartman, 2011, 2014), a 24 Ma ous incision in immediately contiguous areas. scape formed by the northeastward recession of Oligo cene ash bed in the Peach Springs mem- an erosional scarp resulting from the juxtaposi- ber of the Buck and Doe Conglomerate (Young CUESTA-SCARP LANDSCAPE OF tion of weak and strong strata (Garner, 1974; et al., 2011), the 18.78 Ma Peach Spring Tuff THE HUALAPAI PLATEAU Chorley et al., 1984; Young and Wray, 2000). In (Ferguson et al., 2013), and two ca. 19 Ma ages such a classic, structurally controlled landscape, on basalt fl ows located on the Hualapai Plateau The stratigraphic and structural controls that the secondary consequent and resequent streams near Peach Springs and at Separation Canyon shaped the western Grand Canyon region differ and their major tributaries would be constrained (Wenrich et al., 1995). from those that determined the Colorado River’s to follow the northeast structural slope until they Near Long Point (Fig. 1), freshwater lime- course elsewhere on the Colorado Plateau in encountered the next resistant layer, which in stones up to 30 m thick that crop out in the Arizona (Young, 1982, 1985). The strike-paral- this case was near the base of the Kaibab-capped upper portion of the erosionally truncated Music lel western Grand Canyon, augmented by tribu- Shivwits scarp at a transient Paleocene(?) posi- Mountain Formation suggest that Laramide tary runoff from the northeast-dipping Hualapai tion during the regional unroofi ng of the adja- structures were effective in more broadly pond- Plateau strata, trends northwest, parallel to the cent Laramide uplift. Occasional trunk streams, ing the Laramide drainage on the western Colo- base of the recessional Shivwits Plateau scarp such as the Peach Springs paleochannel, must rado Plateau (Young, 1982; Young and Hartman, (Figs. 1 and 2). The north and south canyon rims eventually cross through such regional scarps 2011). Deformation along the Kaibab upwarp or in this area differ both stratigraphically and in in order to allow the effective excavation or the Supai monocline, parallel to Cataract Creek, elevation by 365 m (1200 ft), i.e., the relief on downwasting of the regional landscape. In this could have dammed Laramide drainage north of the scarp that forms the southwest-facing edge regard, the course of the Peach Springs Canyon paleo channel through the presumed topographic TABLE 1. 40Ar/ 39Ar ANALYTICAL DATA barrier was predetermined, in part, by the topo- 36 39 39 40 σ graphic and structural irregularities coincident Power Ar/ Ar ArK Ar* Age ±1 ID (W) 40Ar/39Ar 37Ar/39Ar (×10–3) (×10–15 mol) K/Ca (%) (Ma) (Ma) with the Hurricane fault trend, the site of an older RAY-PS-09-1 san, J = 0.0023441% ± 0.04%, D = 1.006 ± 0.001, NM-231B, Lab# = 59478 east-verging monocline (Young and Huntoon, 14A 2.8 5.777 0.0062 0.2017 20.827 82.0 99.0 23.979 0.045 1987; Young, 1989b; Elston and Young, 1991; 08A 2.8 5.757 0.0060 0.0922 25.752 85.1 99.5 24.029 0.039 05A 2.8 5.768 0.0063 0.0831 16.948 80.7 99.6 24.087 0.046 Huntoon et al., 1981). 01A 2.8 5.783 0.0060 0.1280 17.706 85.5 99.4 24.096 0.044 The Milkweed-Hindu paleochannel could 11A 2.8 5.815 0.0059 0.2255 14.304 85.9 98.9 24.109 0.048 10A 2.8 5.783 0.0060 0.1089 19.875 84.4 99.5 24.117 0.045 only have been incised into the central Huala- 03A 2.8 5.757 0.0065 0.0132 16.315 78.2 99.9 24.127 0.047 pai Plateau surface at the preserved stratigraphic 15A 2.8 5.926 0.0064 0.5878 16.575 79.6 97.1 24.127 0.044 level after the Mesozoic and Upper Paleozoic 04A 2.8 5.859 0.0058 0.3589 28.392 88.0 98.2 24.128 0.041 07A 2.8 5.800 0.0067 0.1406 16.477 76.3 99.3 24.152 0.046 rocks had been stripped down to the level of 13A 2.8 5.774 0.0061 0.0446 20.014 83.4 99.8 24.161 0.042 the lower Supai Group strata and Redwall 02A 2.8 5.867 0.0060 0.3453 10.824 85.0 98.3 24.180 0.061 Limestone (Figs. 3 and 4) in Late Cretaceous 09A 2.8 5.773 0.0082 0.0249 13.292 62.5 99.9 24.182 0.049 06A 2.8 5.799 0.0060 0.1091 14.196 85.7 99.5 24.185 0.050 or Paleocene time, an episode accompanied 12A 2.8 5.804 0.0075 0.0800 18.179 67.8 99.6 24.242 0.048 by the regional recession of the Shivwits scarp σ Mean age ±2 n = 15 24.121 0.039 to a position that must have been much closer Note: Analytical data for recalculation of age (24.12 ± 0.04 Ma) of volcanic ash from upper part of Peach Springs member of the Buck and Doe Conglomerate as corrected from preliminary age (23.97 ± 0.03 Ma) to the location of the modern Colorado River originally published in Young et al. (2011). Isotopic ratios are corrected for blank, radioactive decay, and mass gorge. The distance from the Laramide scarp discrimination; not corrected for interfering reactions. Errors quoted for individual analyses include analytical error edge southward to the Hindu channel at that only, without interfering reaction or J uncertainties. Mean age is weighted mean age of Taylor (1982). Mean age error is weighted error of the mean (Taylor, 1982), multiplied by the root of the mean square of weighted deviates time would have been dependent on the distance (MSWD), where MSWD > 1, and also incorporates uncertainty in J factors and irradiation correction uncertainties. that the bedrock pediment and alluvial fans Decay constants and isotopic abundances are after Steiger and Jäger (1977). Ages are calculated relative to λ extended outward from the vertical scarp face, FC-2 Fish Canyon Tuff sanidine interlaboratory standard at 28.201 Ma. Decay constant ( K[total]) = 5.543e–10/yr. 39 37 36 37 38 39 Correction factors: ( Ar/ Ar)Ca = 0.0007 ± 2e–06; ( Ar/ Ar)Ca = 0.00028 ± 2e–05; ( Ar/ Ar)K = 0.013; which is as much as 1–2 km along the modern 40 39 ( Ar/ Ar)K = 0.01 ± 0.002. scarp. The elevation and regional extent of the

Geosphere, August 2014 667

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Young and Crow

Shivwits Plateau 6060 ft (1845 m) N Cap Rocks: Kaibab Fm Kaibab Shivwits Toroweap F Kelly Point Coconino Plateau E Formations Scarp Miocene basalt Margin 19 Ma Supai through Hermit Formations Separation Canyon

Buck and Doe Fm. Eocene(?)-Oligocene 4900 ft Hindu Fanglomerate (1493 m) Figure 3. Map of Separation- Paleogene Canyon Bridge-Hindu Canyon portion of central Hualapai Plateau, Music Mt. Fm. Ri with distribution of key out- K(?)-Paleogene m Inferred ine crops of Hindu Fanglomerate l on and Buck and Doe Conglomer- Lower Supai Group

ate illustrated in other ﬁ gures. ssecti Dotted cross section line (E-C- Cros B-D) is location of Figure 4. Hindu Canyon Scarp Location ? Scarp Recession Distance South Separation Canyon (SSC) is informal designation for fault Gorge Inner Gorge Rocks 1200 line canyon aligned with better- Inner Redwall Ls. ft known Separation Canyon on through 365 m Grand north side of Colorado River. Precambrian A—location of cobbles in Fig- U D Canyon 11 ure 11. B—location of Figures SS 3 10B and 10C. Not all very small 35.83°N .5°W

C existing outcrops of Hindu Fan- Canyon glomerate in lower half of ﬁ g- Bridge Rim ure can be accurately shown at this scale. F—tributary canyon Separation Canyon Hill (4936 ft,1505 m) labeled on Figure 2. C

4840 ft HUALAPAI (1475 m) PLATEAU

Spencer Canyon A

Map B ) Location m 128 State 1 km D of ft (1 Arizona Hindu3700 Canyon

668 Geosphere, August 2014

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Paleogene Grand Canyon unlikely

GENERALIZED DIAGRAMMATIC CROSS-SECTION VIEW (ECBD) FROM FIGURE 3 SW Not to scale: Small features exaggerated for Clarity NE Distance E-D is Approximately 21 Km Shivwits Plateau Scarp E 1845 m Hindu Canyon HUALAPAI PLATEAU Projected Hindu Canyon Kaibab Laramide Scarp Location (Early Paleogene?) Toroweap Coconino Channel Source of Distinctive Light Buck and Doe Separation Hill basalt Hindu Fanglomerate Conglomerate Clasts in Hindu 1475 m C Fanglomerate Supai Group D B Lower Supai Group Grand Music Canyon Mt. Fm. Redwall Limestone Temple Butte 1128 m Tonto Group (Tapeats/Bright Angel/Muav)

Shivwits Scarp Recession Presumed Equal Precambrian Basement To Distance Between Hindu and Grand Canyon 365 m

Figure 4. Diagrammatic cross section from Figure 3 showing proposed scarp recession from Laramide position to modern Shivwits scarp and key rock units discussed in text. Yellow color serves to emphasize connection of light-colored Shivwits Plateau cap rocks to clasts in Hindu Fanglomerate on opposite side of modern Colorado River gorge.

former stripped surface that now forms the cen- The Hindu reach of the Milkweed-Hindu its junction with Hindu Canyon (Young, 1999; tral Hualapai Plateau can be reasonably inferred paleocanyon system, 8 km south of Grand Can- Huntoon, 1981). The related but deeply buried from the extensive distribution of the Oligocene yon, was the major western tributary for the paleocanyon segment directly beneath the town Buck and Doe Conglomerate and early Miocene northeast-fl owing Hualapai Plateau drainage of Peach Springs was also dammed by mono- volcanic fl ow remnants (Young, 1966; Wenrich system (Fig. 1) until the Laramide monoclinal clinal deformation in Paleocene or early Eocene et al., 1996; Billingsley et al., 1999). damming of lower Milkweed Canyon above time (Young, 1979, 2011). The formation of thick freshwater limestones (14 m and 118 m, respectively) within these two channels on the up-gradient sides of both monoclines is con- Milkweed Canyon, DIAGRAMMATIC CORRELATION Peach Springs vincing evidence for the temporal relationship Hindu Canyon, OF TERTIARY STRATIGRAPHY Wash, Hurricane Bridge Canyon ACROSS HUALAPAI PLATEAU Fault Area between the monoclinal deformation and the (With approximate elevations of top, base) Laramide drainage disruption (Young, 1979, Areas 1505 m 1490 m 2011). The widely distributed monoclines of Coyote Spring the Colorado Plateau have been shown to be Coyote Spring MIDDLE MIOCENE-EARLY PLIOCENE Formation uniquely compressional Laramide features Formation Basalts (Huntoon, 1981), and the stratigraphic record 18–19 Ma implies a geologically abrupt termination of the EARLY MIOCENE previously through-fl owing drainage. Basalts 18.78 Ma Peach Spring Tuff Buck and Doe 18–19 Ma Ash Bed Conglomerate SCARP RECESSION RATES Buck and Doe ± 24.12 0.04 Ma (Peach Sp. mbr.) Conglomerate Sedimentary scarps do not remain in fi xed (Milkweed mbr.) MIDDLE EOCENE-OLIGOCENE (Milkweed mbr.) positions during long intervals of geologic West Water Fm. horizon: Soil; marl. time. Their very existence demonstrates that scarp recession is, and has been, a global geo- Music Mt. Hindu Fanglomerate Music Mt. morphic phenomenon, regardless of whether Formation PALEOCENE-EARLY EOCENE Formation the local climate was arid, semiarid, or humid 1095 m 1130 m (Prince et al., 2010). Global studies of modern scarp recession rates have focused recently on Figure 5. Simplifi ed correlation chart for Tertiary stratigraphy on Hualapai Plateau. Gray the controversy between the relative signifi - shade indicates fl uvial conglomerates or fanglomerates of local derivation. Brick pattern cance of vertical erosion as compared with lat- depicts schematic freshwater limestone intervals caused by structural dams. Source of eral scarp recession along major continental rift 24.12 ± 0.04 Ma ash is possibly Aquarius Mountains, labeled on Figure 1 (Young et al., 2011). margins (Matmon et al., 2002; Gilchrist et al.,

Geosphere, August 2014 669

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Young and Crow

1994; Moore and Blenkinsop, 2006; Kale, have been as rapid as 5–10 km/m.y. Steckler interim Laramide location is presumed to have 2010). Kooi and Beaumont (1994) concluded and Omar (1994) projected average rates of defl ected the paleodrainage at Hindu Canyon that scarp recession is more likely to occur on scarp recession of 6 km/m.y. along the Red Sea eastward toward the trunk canyon that paralleled scarps that are also drainage divides. There rift. Studies of the Drakensberg escarpment by the modern Hurricane fault. This is inferred also is evidence that some major scarps do not Brown et al. (2002) indicated a retreat rate of from the dual facts that (1) scarps cannot remain always undergo the signifi cant degree of lateral 100–200 m/m.y. This rate is similar to the maxi- stationary through long intervals, and (2) the retreat originally argued by King (1953), such mum rate of 95 m/m.y. proposed by Fleming modern Colorado River gorge is parallel to, but as the slow evolution of the Darling escarpment et al. (1999) for the same feature. These stud- 8 km north of, the older Hindu Canyon paleo- of western Australia, proposed by Jakica et al. ies suggest that earlier, qualitative estimates are channel (Figs. 1, 3, and 4). The logical assump- (2011). However, the dramatic “Grand Stair- near the low end of the possible range. However, tion is that the modern Colorado River canyon case” physiography of northern Arizona and even modest erosion rates obviously will cause was constrained to have formed in an identical southeastern Utah demonstrates that regional scarps to migrate signifi cantly over millions of scarp-controlled position as did the older Hindu scarp recession was an important aspect of lat- years, especially where relatively weak shale Canyon, although fl owing in the opposite direc- est Cretaceous and Cenozoic Colorado Plateau substrates strongly infl uence the failure mode of tion (Figs. 1 and 4). Incision of scarp-parallel history. Schmidt (1989) estimated the average more resistant cap rocks, such as on the Huala- canyons for both drainage systems would be scarp recession rates for a number of prominent pai Plateau. inevitable, given the step-bench topography and Colorado Plateau scarps and concluded that northeast-fl owing tributary drainage that char- variable recession rates are controlled by the Scarp Recession and Hualapai acterize the northeast-dipping bedrock platform relative thickness and lithologic attributes of the Plateau Drainage History (Young, 2008). However, scarp-parallel canyons resistant cap rocks, a view shared by Moore and do not form at the immediate base of a vertical Blenkinsop (2006) for southern Africa. Given the global evidence that sedimentary scarp having signifi cant relief in a cuesta-scarp Historically, very few precise estimates of scarps retreat signifi cantly throughout long landscape. The natural slopes created by mass actual scarp recession rates were published prior periods of geologic time, the modern Shivwits wasting and overland fl ow processes distribute to 2000, except in areas partially covered by Plateau scarp could not have remained in a fi xed colluvial material along a natural and predict- dated volcanic rocks (Young and Wray, 2000), position between the initiation of the Laramide- able range of pediment profi les that must, by in locations containing uniquely located packrat age Hindu Canyon channel and the conven- simple inspection of existing landscapes, extend nests (Cole and Mayer, 1982), by a combination tionally cited time of late Miocene or Pliocene hundreds of meters to a kilometer or more out- of qualitative morphometric and stratigraphic Grand Canyon incision, irrespective of how ward from any vertical scarp face having hun- analysis (Schmidt, 1989), or where suitable slow the actual cliff recession rate may have dreds of meters of relief, such as the Shivwits radiocarbon samples were available (Gutier- been. Put another way, if an ancestral western Plateau margin. The position of such rivers, rez et al., 1998). Australian scarps in volcanic- Grand Canyon had existed in its current loca- prior to incision, will always be located near the capped sedimentary strata have retreated at rates tion as long as 70 m.y. ago, the Shivwits scarp infl ection point between the natural dip or slope of 125–250 m/m.y. (Young and Wray, 2000). would not currently be in such close proximity of the rocks below and the opposing slope of the Moore and Blenkinsop (2006) discussed the (3–5 km) to the northern canyon rim. It could colluvial debris and alluvial fans that currently extensive literature on the resistant Drakensberg have retreated some 14 km at even a modest rate extend as much as 1–2 km outward from the scarp of southern Africa and its estimated retreat of 200 m/m.y., based on the studies cited previ- face of the existing Shivwits scarp. rate since Late Cretaceous time of between 330 ously. This calculation does not include allow- Furthermore, the development of erosional and 435 m/m.y. Schmidt (1989) calculated a ance for the 1–2 km distance from the scarp reentrants formed by irregular headward ero- 500 m/m.y. recession rate in Arizona for the edge down to the base of the adjacent alluvial sion by competing scarp-face drainages will Kaibab Formation scarp, which agrees reason- slope, the closest distance from the scarp face logically expand with time as the scarp retreats. ably with the 450 m/m.y. fi gure cited by Cole at which a regional subsequent stream would The irregularities in a modern scarp such as the and Mayer (1982) for the same formation using likely form. The evidence of modern Shivwits Shivwits must be much greater now than when an alternative approach. Gutierrez et al. (1998) Plateau scarp recession also can be appreciated the scarp was located at a more southerly posi- used radiocarbon dating of surfaces on talus fl at- by considering the widespread volume of coarse tion, nearer Hindu Canyon. Headward erosion irons over a 35,000 yr interval to measure scarp colluvial material currently spreading south- has resulted in the random capture of dip-par- retreat rates on semiarid Spanish scarps of 0.9– ward from the scarp face. Simply restoring this allel drainages previously fl owing north on the 1.0 km/m.y. These semiquantitative data sug- geologically young mobile sheet of debris to the Shivwits Plateau proper, a factor that contributes gest that lateral scarp recession rates between scarp face would obviously restore the escarp- to scarp irregularity by increasing the effective 125 and 500 m/m.y. (0.125–0.5 mm/yr) are rea- ment to a position slightly south of its current power of the scarp-face streams that fortuitously sonable and likely include the slow end of the location over the short term. capture the largest share of the available north- scarp recession range for moderately resistant Why would an ancestral Grand Canyon, par- fl owing drainage above and behind the scarp. cap rocks overlying weaker shales, such as the allel to Hindu Canyon, be an unlikely compo- Kaibab scarp of the Shivwits Plateau. nent of the Laramide drainage? The logic and LARAMIDE INHERITANCE AND More recently, the newer age dating tech- fi eld evidence are inferred from the following GEOLOGIC CONSTRAINTS niques that use cosmogenic isotopes and fi ssion- observations. The basic structure and geomor- track methods have provided more quantitative phology of the modern Hualapai Plateau and its Space Constraint measures of the average rates of scarp recession abandoned Laramide paleocanyons imply that in different terranes. Persano et al. (2002) pro- the position of the scarp defi ning the southern The widespread late Eocene(?)–Oligocene posed that the escarpment retreat rate on the margin of the Shivwits Plateau was ~8 km to Buck and Doe Conglomerate, the remnants Great Escarpment in southeast Australia may the southwest of its current position when that of which cover the Hualapai Plateau up to the

670 Geosphere, August 2014

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Paleogene Grand Canyon unlikely

very edge of the modern Colorado River canyon, indicate that post-Laramide incision was delayed until well after a lengthy Early Ter- tiary episode of fl uvial deposition, followed by Miocene volcanism, the upper limit of which is minimally constrained by emplacement of the widespread Peach Spring Tuff and associated basalts, as well as abundant younger Miocene fl uvial sediments (Fig. 5). Miocene basalt fl ow remnants capping Buck and Doe Conglomer- ate on the south rim of Grand Canyon, next to south Separation Canyon (Separation Hill basalt, 19.0 ± 0.4 Ma; Wenrich et al., 1995), demonstrate that the Laramide paleocanyons were fi lled with Oligocene sediments deposited by northeast-fl owing tributaries, before being capped by Miocene Peach Spring Tuff and other local basalt fl ows (Fig. 6). The greater part of the preexisting Laramide canyon relief was essen- tially buried by early Miocene time (ca. 19 Ma). (Clarifi cation: Modern U.S. Geological Survey topographic maps [1:24,000], unlike historic maps, show Separation Canyon as consisting Figure 6. Separation Hill basalt (upper right) capping outcrop of Buck and Doe Conglomer- of two aligned, fault-controlled, segments that ate, Milkweed member. First two dark ledges at top of hill are basalt; third ledge down is are located on opposite sides of Grand Can- Buck and Doe Conglomerate. Kelly Point on Shivwits Plateau is on horizon at center right. yon [Fig. 1], as opposed to the name originally Rim of south Separation Canyon is at lower left. Person at right center for scale is standing being applied only to the much longer northern on lower Supai Group rocks. tributary, as described in older publications and made famous by the Powell expedition. The smaller tributary near Bridge Canyon is referred frame provides broad limits between 20 and the Hualapai Plateau so as to create suffi cient to informally as “south Separation Canyon” to 60 Ma for the 8 km of scarp recession, which space for an entirely new, post-Hindu drainage avoid confusion in this discussion.) translates to an average recession rate of between to form in the current location of the modern The locations of the Separation Hill basalt 400 and 135 m/m.y. Such erosion rates are Grand Canyon gorge. Assuming the Laramide and its source vent, now on opposite sides of the entirely consistent with the published range of Milkweed-Hindu paleodrainage was established 730-m-deep Spencer Canyon, also demonstrate moderate scarp recession rates previously cited. no later than late Paleocene time, but probably that the central Hualapai Plateau was relatively If one assumes a moderate, intermediate rate earlier, it seems clear that cliff recession suffi - fl at and featureless and lacked any signifi cant of scarp recession of 200 m/m.y., the Shivwits cient to allow the Grand Canyon to form 8 km tributary relief that would have prevented the cliffs, capped by Kaibab limestone, would have further north most likely involved some tens of relatively thin lava fl ows from reaching the Sep- retreated 8 km in ~40 m.y. (Fig. 4). Forty mil- millions of years. This physiographic constraint aration Hill locality (Young, 2011). The erup- lion years is consistent with the evidence that does not allow for any deep, proto–Grand tive center mapped by Billingsley et al. (1999), Hindu Canyon has been inactive since drain- Canyon to form in its current location prior to located 13 km southwest of the head of south age was tectonically disrupted, no later than Oligo cene time (34–23 Ma) at the very earliest, Separation Canyon and on the opposite side of middle Eocene time (40–48 Ma ago). Using the assuming even a modest rate for necessary scarp Spencer Canyon, is the only basalt source in faster 450–500 m/m.y. rates for Kaibab scarps recession. Logically, and from a classic geomor- the vicinity with an elevation suffi ciently high estimated by Cole and Mayer (1982) and by phologic perspective, there would be no need, (1516 m [4975 ft]) to allow the preserved fl ow Schmidt (1989) would reduce the recession nor suffi cient runoff, for two such large, parallel, remnants to have reached their current position time to 16–18 m.y. These admittedly qualitative and competing canyons to have formed simulta- (1504 m [4936 ft]) capping Separation Hill. geomorphic relationships imply that the western neously in their current positions. The 8 km north-south separation of the mod- Grand Canyon could not have formed north of Furthermore, the formation of any pro- ern Grand Canyon from the older Hindu Can- the comparable Laramide paleochannel at Hindu posed deep ancestral Grand Canyon should be yon paleochannel is the indirect measure of Canyon until the Shivwits scarp had retreated refl ected by the coincident onset of necessary the amount of scarp recession that must have at least 8 km from its intermediate Laramide and integrated tributary incision throughout the occurred between the inception of Laramide (Hindu) position, which is assumed to have Hualapai Plateau, rather than the observed epi- drainage and the beginning of modern Grand shaped the right-angle eastward defl ection from sode of Paleocene–Miocene aggradation, which Canyon incision (Fig. 4). The time interval dur- Milkweed Canyon into Hindu Canyon. Obvi- is widely preserved throughout the closed basins ing which the scarp recession of 8 km occurred ously, this interval of scarp recession could only and across the beveled surface of the Hualapai can be constrained, at a minimum, between late have begun following the initial establishment Plateau, including the small erosional remnants Oligocene time and 5 Ma, the conventionally of the Hindu channel. Thus, the physical cir- of sediments and lavas preserved at Separation cited onset of Colorado River incision, or back cumstances require a signifi cant post-Paleocene Hill, only 1200 m south of the modern Grand to early Paleocene time at a maximum. This time interval of scarp recession necessary to widen Canyon rim (Figs. 3, 4, and 6). Such necessary,

Geosphere, August 2014 671

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Young and Crow

supportive tributary development would natu- Springs Wash and into the adjacent Truxton Val- tinuously accumulating throughout the lower rally evolve on the northeast structural slope of ley. The upper arkosic Peach Springs member elevations of the plateau during much of Paleo- the Hualapai Plateau, especially if the implied of the Buck and Doe Conglomerate is relatively gene time. The only conspicuous depositional time frame were as long as 70 m.y. localized but ranges up to 75 m (250 ft) thick hiatus, preserved as a thick red soil horizon at Although this simplistic analysis, based on in Peach Springs Wash, the headward reach of the top of the Music Mountain Formation (Figs. dated volcanic units, geomorphic relations, esti- Peach Springs Canyon. The lower Milkweed 5 and 9), seems to mark a period of low sedi- mated scarp recession rates, and stream capture, member is thinner near Peach Springs but ment production, but not necessarily measurable fi ts the approximate timing of established geo- thicker and more widespread throughout the erosion or drainage incision. This depositional logic events for the interval in question, more central Hualapai Plateau. The Peach Springs hiatus, or paraconformity, clearly marked by an direct evidence also precludes any incised, member contains a volcanic ash (Fig. 7) located abrupt and distinctive upward red-to-buff color ancestral Grand Canyon from occupying its cur- ~2 m from its upper contact near the town of transition, may simply mark the Eocene-Oligo- rent position near Separation and Bridge Can- Peach Springs. The originally reported Oligo- cene transition from subtropical conditions to a yons until well after late Oligocene time. cene age of this ash (23.97 ± 0.03 Ma; Young local climate that is documented regionally and et al., 2011) was recalculated as 24.12 ± 0.04 Ma globally as recording marked cooling followed Stratigraphic Constraints in the Bridge- using the new Fish Canyon sanidine monitor by increasing aridity (Prothero and Berggren, Separation-Hindu Canyon Region age of 28.201 Ma (Kuiper et al., 2008; Fig. 8; 1992). Peterson and Abbott (1979) described see Appendix 1). A potential source for the ash the Paleocene–Eocene paleosol sequences of As previously noted, the Music Mountain is the Aquarius Mountains (Fig. 1; Young and nearby southwestern California also as record- Formation interfi ngers laterally with the pene- McKee, 1978). The ash, located so high in the ing a widespread change from Paleocene tropi- contemporaneous Hindu Fanglomerate of local 420-m-thick Tertiary section (Young, 2011), cal lateritic soils to a semiarid climate beginning derivation (Fig. 5), and both are capped by the lends further credence to the other evidence in late middle Eocene time, and based, in part, locally derived Buck and Doe Conglomerate for the Eocene or older age of the underlying, on changes in clay mineralogy. in the region where tributaries to Separation, more deeply weathered Tertiary sequence on the The sources for the basal Milkweed member Bridge, and Hindu Canyons are in close proxim- Hualapai Plateau (Young and Hartman, 2011). of the Buck and Doe Conglomerate in the Sepa- ity, as shown on Figures 3 and 4 (Young, 1989a; The distribution of the Buck and Doe Con- ration-Bridge-Hindu Canyon divide region were Billingsley et al., 1999; Elston and Young, 1991). glomerate and the Oligocene age of the upper- the Paleozoic rocks exposed along the more Buck and Doe Conglomerate remnants (Figs. 3 most beds of the Peach Springs member clearly elevated southwestern edge of the Colorado and 4) mark the low-relief aggradational surface attest to the fact that fl uvial sediments were con- Plateau or southern Grand Wash Cliffs, locally extending across much of the central Hualapai Plateau northwest of Peach Springs Canyon at a surface elevation between 1460 and 1430 m (4800–4700 ft). The locally derived Buck and Doe gravels spilled out across the local divides up to, and probably beyond, the encroaching erosional rims of modern Separation and Bridge Canyons immediately prior to the onset of widespread Miocene volcanism, as documented by the position of the 19 Ma Separation Hill basalt and underlying Buck and Doe gravel (Figs. 3, 4, and 6). This episode of fl uvial aggradation, which followed the deposition of the Music Mountain Formation and the Hindu Fanglomer- C ate, is uninterrupted by any evidence of local or regional incision by Hualapai Plateau drainages, B even at the very rim of the western Grand Can- yon gorge, and as further documented by the undisturbed stratigraphic sequences preserved in the structurally closed basins in Milkweed, Hindu, and Peach Springs Canyons. The contact between the two informally des- ignated members of the Buck and Doe Con- glomerate (Fig. 5) can be traced northwest from Peach Springs Canyon to a position ~6 km southeast of Bridge Canyon on the broad divide between Hindu and Peach Springs Canyons (Fig. 1). The juxtaposition, uniform contact, and Figure 7. Location of late Oligocene ash bed (24.12 ± 0.04 Ma) in Peach Springs Wash. distribution of the two members demonstrate Arrow indicates 10-cm-thick white ash layer near top of Peach Springs member of Buck that they formed in close succession, refl ect- and Doe Conglomerate (B). Slope forming unit above B is Coyote Spring Formation (C). ing only the headward expansion of the post- Stratigraphic details are given in Young (1999, 2011). Location: 35.553°N, 113.412°W (U.S. Laramide drainage southwestward from Peach Geological Survey Peach Springs Topographic Quadrangle Map, scale 1:24,000).

672 Geosphere, August 2014

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Paleogene Grand Canyon unlikely

101 There are several more very small outcrops of 100 the fanglomerate in the vicinity of Bridge and 99 Separation Canyons than realistically can be 40 98 shown on Figures 3 and 4. % Ar* 97 Shivwits Plateau Source of 96 100 Hindu Fanglomerate 90 80 The color of the Hindu Fanglomerate con-

70 K/Ca trasts with the enclosing formations because 60 of its thoroughly oxidized matrix, although the typical orange hue occasionally appears some- 50 100 what bleached at more weathered exposures (Figs. 10B and 10C). In the broad upland surface between south Separation and Bridge Can- 90 yons (Figs. 3 and 10A), the scattered remnants of Hindu Fanglomerate preserved beneath the 80 Buck and Doe Conglomerate show obvious imbrication (Fig. 11) documenting southward 70 transport and clearly represent the distal portions of broad alluvial and debris fans that built 60 southward from the distant Shivwits Plateau scarp, similar to the modern fans that extend

50 southward from the Shivwits scarp today (Fig. 12). The fanglomerate in this restricted upland Probability (Fig. 3) contains numerous conspicuous light- 40 colored cobbles (Fig. 11) that could only have been derived from the more resistant Coconino, 30 Toroweap, and Kaibab Formations that crop out only to the north of the Grand Canyon where 20 they cap the Shivwits Plateau scarp (Figs. 4 and 12). The readily identifi able Coconino Sand- 10 stone thins westward and is no longer a signifi - 24.12 ± 0.04, MSWD = 2.12, Prob. = 0.01 cant source for clasts west of Kelly Point at the Bridge Canyon longitude (Wenrich et al., 1996). 0 23.85 23.95 24.05 24.15 24.25 24.35 However, the Toroweap and Kaibab Forma- tions also include conspicuous, light-colored Age (Ma) sandy beds, sandy limestones, and sandy dolo- stones within the upper 120–150 m (400–500 ft) Figure 8. Age probability plot of ash bed (24.12 ± 0.04 Ma) near top of Peach Springs mem- of the Shivwits scarp north of Grand Canyon, ber of Buck and Doe Conglomerate in Peach Springs Wash from single-crystal laser-fusion where they contrast sharply with the underly- results for 15 sanidine crystals. MSWD—mean square weighted deviation. See Appendix 1 ing Permian red beds (Figs. 2 and 12). No other for methods. similar rock types occur lower in the Paleozoic section south of Grand Canyon, nor are any similar clast lithologies present in the southwesterly referred to as the “Music Mountains” (Fig. 1). Between the modern Colorado River gorge derived Music Mountain or Buck and Doe for- This includes clasts from the Tapeats through and the Hindu Canyon paleochannel, in the mations. The clast imbrication at several small the Redwall formations, which cover most of the vicinity of south Separation and Bridge Can- exposures scattered throughout the Bridge- adjacent Hualapai Plateau. The sharp lithologic yons, the lower Buck and Doe Conglomerate is Separation Canyon region (Fig. 11) combined transition from exotic (arkosic) Music Mountain preserved as remnants of a relatively fl at deposi- with the conspicuous light-colored clasts clearly to local Paleozoic formation clasts of the Buck tional surface near 1455 m (4775 ft) in elevation document a northerly source for the weakly and Doe Conglomerate throughout the Laramide (Figs. 3, 4, and 10). In this region, adjacent to stratifi ed Hindu Fanglomerate, namely, the channel system suggests that prevolcanic (pre– the Laramide paleochannel proper, the Milk- Shivwits scarp that forms the northern side of late Oligocene) faulting along the southern Hual- weed member directly overlies several small western Grand Canyon. The modern Shivwits apai Plateau margin may have begun somewhat scattered remnants of the Hindu Fanglomerate scarp fans that provide the closest approxima- earlier than the typically cited mid-Miocene (Fig. 10), the lateral equivalent of the Music tion of Laramide transport conditions, but in Basin and Range extension episode. Rocks in the Mountain Formation, which typically consists a Quaternary climatic setting, were probably Whipple tilt block domain south of Lake Mead of weakly stratifi ed colluvium, debris-fl ow, and more active during the Pleistocene, but are cur- show that faulting began in the interval between similar mass-wasting deposits shed into the rently undergoing marked headward dissection 32 and 22 Ma (Spencer and Reynolds, 1989). Laramide channels from adjacent elevations. under the prevailing semiarid conditions, com-

Geosphere, August 2014 673

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Young and Crow

In a similar fashion, the more effective headward erosion by the much longer Spencer Can- yon (Figs. 1 and 3) has completely severed the Laramide connection of Milkweed to Hindu Canyon and reversed the western Hindu Canyon drainage to its present westward course, leaving only a much shorter eastern segment, Lost Man Canyon, to drain eastward into Peach Springs Canyon. Spencer Canyon appears to have had a structurally determined hydrologic advantage due to its close parallelism to the east-verging Meriwhitica monocline (Huntoon, 1981).

Pliocene Erosion Rate at Bridge Canyon

If the western Grand Canyon has only existed since early Pliocene time, any tributaries that have no structural advantage and that have expanded primarily due to simple headward erosion should have a volume and area proportional to this relatively short time frame. Bridge Can- yon, below its distinctive rim, has a volume of ~2.85 km3 with a drainage area of 20 km2 (Fig. 13). Is it reasonable that erosion could produce a tributary canyon of this size in fi ve million Figure 9. Paraconformity contact (depositional hiatus, also termed West Water soil horizon) years? Quantitative studies of sediment yields in between weathered red Paleocene(?)–early Eocene Music Mountain Formation and overly- arid regions indicate that basins of this relatively ing Milkweed member of Buck and Doe Conglomerate of late Eocene(?)–Oligocene age. small size typically produce between 100 and Location is 410 m southwest and 65 m below ash horizon shown in Figure 8. 800 metric tons of sediment per square kilometer per year (Griffi ths et al., 2006; Clapp et al., 2000). Using these estimates, it would require bined with incision by steep modern Colorado some speculate that a large precursor to Grand removal of an average volume of between 1 and River tributaries (Fig. 12). Elsewhere, through- Canyon was already in existence (Flowers and 2 m3/d in order to create a feature the size of out the Hualapai Plateau paleocanyon system, Farley, 2012; Wernicke, 2011). The fi eld evi- Bridge Canyon in 5 m.y. Given the canyon and the Hindu Fanglomerate clearly represents local dence for this long-term sediment aggradation basin dimensions and an average limestone den- valley-slope mass-wasting deposits with no evi- from both directions, the southwestern Hualapai sity of 2600 kg/m3, this would require an amount dence of extremely well-rounded or far-traveled Plateau margin and the Shivwits Plateau scarp, of sediment removal of ~50–100 metric tons/yr lithologies. clearly precludes the formation or existence of for each square kilometer of basin area. These The Hindu Fanglomerate provenance and dis- an incised, through-fl owing drainage system fi gures are near the low end of the range of mod- persal pattern near south Separation and Bridge crossing the Hualapai Plateau in the western ern sediment production rates for drainages in Canyons preclude the existence of any signifi - Grand Canyon region between Paleocene and arid regions, and they disregard any additional cant canyon incision by a river in the current early Miocene time. volume of bedrock that would be removed by location of the western Grand Canyon during solution in such a predominantly carbonate ter- fan construction. The general time limits estab- MIOCENE–PLIOCENE INCISION rane. This implies that the relatively short Grand lished for the Hindu Fanglomerate and the Buck IMPLICATIONS Canyon tributaries that characterize much of the and Doe Conglomerate are conservatively estab- western canyon’s south rim could have easily lished as between early Eocene and late Oligo- Modern tributaries, such as those in Spencer formed within the Pliocene time frame pro- cene time, the interval spanning 24–48 Ma. and Bridge Canyons and similar nearby drain- posed, even under arid conditions. Any hypoth- This 24 m.y. interval also is estimated to be ages fl owing north into the Grand Canyon, have esized ancestral Paleogene Grand Canyon a realistic time that would be required for the headwardly eroded and captured remnants of should have developed much longer tributaries Shivwits scarp to recede the 8 km required to the Milkweed-Hindu channel system (Figs. 1 that would have competed with those entering create the necessary space for post–Hindu Can- and 13). This relationship also implies that the the Hindu channel, especially given the natural yon erosion to allow a large ancestral canyon Hindu channel is older than Grand Canyon. The northeast dip slope of the plateau. The numer- to form where Grand Canyon gorge is located classic barbed tributary pattern (Fig. 13) is best ous stream captures, especially those closest to today. However, fi eld relationships clearly developed where 4-km-long Bridge Canyon the Colorado River, and the obvious drainage indicate that the local plateau surface was fi rst has nearly intercepted the main Hindu Canyon immaturity imply that tributary fl ow southward covered by northerly derived alluvial-fan debris paleochannel (Young, 1970). As can be deter- into Hindu Canyon was only interrupted late in of the Hindu Fanglomerate and then capped by mined from the drainage pattern, the barbed the modern incision cycle, rather than tens of southwesterly derived Buck and Doe gravels tributaries were initially captured less than 2 km millions of years ago when the Hindu channel and volcanic rocks during the very time that from the present south rim of Grand Canyon. was the dominant master drainage.

674 Geosphere, August 2014

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Paleogene Grand Canyon unlikely

A SP

GC S SHSH BD

B BC HF 11

Redwall LS

B C Redwall LS

BD HF HF

Figure 10. (A) Aerial view to north from above Hindu Canyon (HC) toward Separation Hill basalt (SH). White letters: GC—Grand Can- yon, SP—Shivwits Plateau, S—Spencer Canyon, BC—Bridge Canyon, HF—Hindu Fanglomerate, BD—Buck and Doe Conglomerate, 11—Figure 11 location; LS—limestone. Locations of photos in B and C are marked with white arrows labeled B and C. Scale: distance from north edge of Hindu Canyon in foreground to Separation Hill is 8 km. (B) Close-up aerial view of contact between Hindu Fanglomerate (HF) and Buck and Doe Conglomerate (BD). Scale: thickness of BD outcrop in cliff near top center of view is 12 m. (C) Hindu Fanglomer- ate (HF) ﬁ lling Laramide tributary to Hindu Canyon. (Location is also marked B on Fig. 3.) Fanglomerate in C is more bleached near base (HF in foreground) but more orange near top of exposure. Scale: thickness of HF from lower foreground to center horizon is 152 m.

Furthermore, the drainage density for the development, and vegetation characteristics of cene depositional events and aggradational exhumed tributaries to the Laramide Hindu Can- the humid Paleogene Epoch when Hindu Can- conditions on the Hualapai Plateau logically yon that are being captured by Bridge Canyon yon and its exhumed, captured tributaries devel- preclude the existence of a Late Cretaceous or reﬂ ects an entirely different dendritic pattern oped as the dominant master drainage at this Early Tertiary, ancestral Grand Canyon coinci- than that created by Grand Canyon tributaries, location. dent with the modern canyon’s present location. which are currently incising into the very same The Shivwits scarp would have been well south bedrock units (Young, 1970). The distinctively CONCLUSION of its current location 60–70 m.y. ago, probably different drainage patterns and drainage densi- covering a substantial portion, if not all, of the ties of the two river systems, which are obvious The combination of geomorphic, strati- location of the modern canyon. Such a scarp on aerial or satellite imagery, are undoubtedly graphic, and chronologic evidence for an location, several kilometers south of its pres- related to the more humid climate, thick soil extended interval of Paleocene through Mio- ent position, would have prevented any ances-

Geosphere, August 2014 675

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Young and Crow

A N

Figure 11. (A) Content of prominent light-colored clasts in Hindu Fanglomerate near Bridge Canyon site (location at white 11 on Fig. 10; location A on Fig. 3). Prominent imbrication indicates ﬂ ow from right (north) to left. Notebook is 23 cm long. (B) Same general location as A. Numerous light-colored clasts in A and B were derived from Kaibab, Toroweap, and Coconino formations capping Shivwits Plateau north of Grand Canyon, as shown in Figure 12. No other source for such clast lithologies exists on Hualapai Plateau south of Grand Canyon gorge, or immediately west of Hualapai Plateau.

tral Grand Canyon from forming in the narrow or Eocene time clearly precludes the presence yon incision in the same vicinity. All of the fi eld space that would have been available north of of an incised older canyon coincident with the evidence summarized in this analysis points to Hindu Canyon. Modest scarp recession rates modern Colorado River gorge. the presence of a late Miocene or Pliocene west- to broaden the plateau surface between Hindu The record of consistent aggradation through- fl owing Colorado River, possibly integrated Canyon and the present Shivwits cliffs would out the Hualapai Plateau, interrupted only by a with, or initiated by, gradual headward erosion require tens of millions of years, beginning no pre-Oligocene weathering episode, and no con- or knick point migration from a drainage basin later than late Paleocene or Eocene time. The spicuous erosion, from early Eocene through with modest proportions and limited runoff on existence of broad, south-sloping alluvial fans late Miocene or early Pliocene time is incom- the western Hualapai Plateau margin during late extending across this same area in Paleocene patible with signifi cant contemporaneous can- Miocene time (Young, 2008).

676 Geosphere, August 2014

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Paleogene Grand Canyon unlikely

Figure 12. View of light-colored Kaibab, Toroweap, and Coconino formations capping Supai Group red beds near Toroweap overlook, east of the Hurricane fault. Dis- sected, light-colored alluvial fans probably were more active during the Pleistocene, and their signiﬁ cant dispersal distance demonstrates why the Hindu Fanglomerate contains light-colored clasts derived from the Shivwits Plateau scarp at locations well south of modern Grand Canyon on the Hualapai Plateau. Lower, light-colored ledge (L) in the center left of view is within the normally red, L upper Esplanade Sandstone, which becomes locally bleached by groundwater due to increased fracturing near major fault zones and breccia pipes. The Esplanade Sandstone crops out only north of the modern gorge on the Hualapai Plateau west of Peach Springs Canyon. Scale: thickness of stratigraphic section from Layer L to top of center horizon is 425 m.

113.5 W Co lor ad o R N iver

Canyon

Bridge Canyon

35.75 N Rim

Capture Locations Hindu Canyon 2 km

Figure 13. Active stream captures of exhumed Laramide drainage by Bridge Canyon and unnamed tributary to the east. Some abandoned valley connections between captured segments remain obvious on aerial photographs and satellite imagery, as at location A.

Geosphere, August 2014 677

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Young and Crow

APPENDIX 1. AR/AR METHODS Clapp, E.M., Bierman, P.R., Schick, A.P., Lekach, J., Enzel, land Basement Tectonics: A Special Issue Dedicated FOR RECALCULATING BUCK AND Y., and Caffee, M., 2000, Sediment yield exceeds sedi- to Donald L. Blackstone, Jr.: University of Wyoming DOE ASH AGE ment production in arid region drainage basins: Geol- Contributions to Geology, v. 19, no. 2, p. 127–134. ogy, v. 28, no. 11, p. 995–998, doi:10 .1130 /0091 -7613 Huntoon, P.W., Billingsley, G.H., and Clark, M.D., 1981, (2000)28 <995: SYESPI>2 .0 .CO;2 . Geologic Map of the Hurricane Fault Zone and Vicin- Sanidine crystals separated from the ash were load- Cole, K.C., and Mayer, L., 1982, Use of packrat middens ity, Western Grand Canyon, Arizona: Grand Canyon, ing into machined aluminum disks and irradiated for to determine rates of cliff retreat in the eastern Grand Arizona, Grand Canyon Natural History Association, 10 h at the U.S. Geological Survey’s Triga reactor, Canyon: Geology, v. 10, no. 11, p. 597–599, doi: 10 scale 1:48,000, 1 sheet. near Denver, Colorado. Single sanidine crystals were .1130 /0091 -7613 (1982)10 <597: UOPMTD>2.0 .CO;2 . Jakica, S., Quigley, M.C., Sandiford, M., Clark, D., Fiﬁ eld,

then fused with a Synard CO2 laser and analyzed in a Cooley, M.E., and Davidson, E.S., 1963, The Mogollon L.K., and Alimanovic, A., 2011, Geomorphic and Mass Analyzer 215–250 mass spectrometer at the New highlands: Their infl uence on Mesozoic and Cenozoic cosmo genic nuclide constraints on escarpment evolu- Mexico Bureau of Geology and Mineral Resources erosion and sedimentation: Arizona Geological Society tion in an intraplate setting, Darling Escarpment, West- Geochronology Research Laboratory. Fish Canyon Digest, v. 6, p. 7–35. ern Australia: Earth Surface Processes and Landforms, Damon, P.E., 1964, Correlation and Chronology of Ore v. 36, no. 4, p. 449–459, doi: 10 .1002 /esp .2058 . Tuff sanidine was used as a neutron fl ux moni tor with Deposits and Volcanic Rocks: Annual Progress Report Kale, V.S., 2010, The Western Ghat: The great escarpment the assigned age of 28.201 Ma (Kuiper et al., 2008). to U.S. Atomic Energy Commission Report No. C00– of India, Ch. 26, in Migon, P., ed., Geomorphologi- J-factors were determined by fusion of approximately 689–42: Tucson, Arizona, University of Arizona, Geo- cal Landscapes of the World: Dordrecht, Netherlands, 6 fl ux monitor single crystals from equally spaced chronology Laboratories, p. 15–17. Springer Science & Business Media, p. 257–264. radial positions around the irradiation tray to a pre- Elston, D.P., and Young, R.A., 1991, Cretaceous–Eocene Karlstrom, K.E., Lee, J., Kelley, S., Crow, R., Young, R.A., cision of 0.04%. Laser sensitivity values, as well as (Laramide) landscape development and Oligocene– Lucchitta, I., Beard, L.S., Dorsey, R., Ricketts, J.W., Pliocene drainage reorganization of Transition Zone Dickinson, W.R., and Crossey, L., 2013, Comment mass discrimination values, for different runs were 4 3 determined by running a series of airs to 4.99e–17 and Colorado Plateau, Arizona: Journal of Geophysi- on “Apatite He/ He and (U-Th)/He evidence for an cal Research, v. 96, no. B7, p. 12,389–12,406, doi: 10 ancient Grand Canyon”: Science, v. 340, p. 143b. mol/pA and 1.005, respectively. Correction factors for .1029 /90JB01978. Karlstrom, K.E., Lee, J., Kelley, S., Crow, R., Crossey, L., interfering reactions were determined from analysis of Faulds, J.E., Feuerbach, C.E., Miller, C.F., and Smith, E.I., Young, R.A., Lazear, G., Beard, L.S., Rickets, J., Fox, K-glass and CaF2. See Figure 8 and Table 1. 2001, Cenozoic evolution of the northern Colorado M., and Shuster, D., 2014, Formation of the Grand River extensional corridor, southern Nevada and north- Canyon 5–6 million years ago via integration of older ACKNOWLEDGMENTS west Arizona, in Erskine, M., et al., eds., The Geologic palaeocanyons: Nature Geoscience, v. 7, p. 239–244, Transition, High Plateaus to Great Basin: A Sympo- doi: 10 .1038 /ngeo2065 . We thank L.S. Beard and anonymous reviewers sium and Field Guide (the Mackin Volume): Utah Geo- Keith, S.B., and Wilt, J.C., 1985, Late Cretaceous and Ceno- for their helpful comments regarding the content and logical Association Publication 30, p. 239–271. zoic orogenesis of Arizona and adjacent regions: A organization of this paper. The logistical support of Ferguson, C.A., McIntosh, W.C., and Miller, C.F., 2013, strato-tectonic approach, in Flores, R.M., and Kaplan, the Frank Hunt family and the cooperation of Loretta Silver Creek caldera—The tectonically dismembered S.S., eds., Cenozoic Paleogeography of West-Central source of the Peach Spring Tuff: Geology, v. 41, p. 3–6, United States: Denver, Rocky Mountain Section, Soci- Jackson-Kelly of the Hualapai Tribe are greatly appre- doi: 10 .1130 /G33551 .1 . ety of Economic Paleontologists and Mineralogists, ciated in facilitating R.A. Young’s long-term studies Fleming, A., Summerfi eld, M.A., Stone, J.O., Fifi eld, L.K., p. 403–437. of the geology of the Hualapai Plateau. P. E. Damon and Cresswell, R.G., 1999, Denudation rates for the King, L.C., 1953, Canons of landscape evolution: Geologi- and E. H. McKee provided the core of the early radio- southern Drakensberg escarpment, SE Africa, derived cal Society of America Bulletin, v. 64, p. 721–751, doi: metric age control that supported the wide-ranging from in-situ–produced cosmogenic 36Cl: Initial results: 10 .1130 /0016 -7606 (1953)64[721: COLE]2.0 .CO;2 . fi eldwork, which might not have been completed Journal of the Geological Society of London, v. 156, Kooi, H., and Beaumont, C., 1994, Escarpment evolution p. 209–212, doi: 10 .1144 /gsjgs .156 .2 .0209 . on high-elevation rifted margins: Insights derived without the use of I. Lucchitta’s faithful Toyota Land 4 3 Cruiser. We are especially indebted to our innumer- Flowers, R.M., and Farley, K.A., 2012, Apatite He/ He and from a surface processes model that combines diffu- (U-Th)/He evidence for an ancient Grand Canyon: sion, advection, and reaction: Journal of Geophysical able Colorado Plateau colleagues for freely sharing Science, v. 338, p. 1616–1619, doi: 10 .1126 /science Research, v. 99, no. B6, p. 12,191–12,209, doi: 10 .1029 their ideas during our many informal discussions and .1229390 . /94JB00047 . joint fi eldtrips involving the history and evolution of Flowers, R.M., and Farley, K.A., 2013, Response to com- Kuiper, K.F., Deino, A., Hilgen, F.J., Krijgsman, W., Renne, the Colorado River region. ments on “Apatite 4He/3He and (U-Th)/He evidence for P.R., and Wijbrans, J.R., 2008, Synchronizing rock an ancient Grand Canyon”: Science, v. 340, p. 143, doi: clocks of Earth history: Science, v. 320, p. 500–504, REFERENCES CITED 10 .1126 /science.1234203 . doi: 10 .1126 /science.1154339 . Flowers, R.M., Wernicke, B.P., and Farley, K.A., 2008, Lucchitta, I., 1966, Cenozoic Geology of the Lake Mead Beard, L.S., and Lucchitta, I., 1993, Geologic Map of the Unroofi ng incision, and uplift history of the southwest- Area Adjacent to the Grand Wash Cliffs, Arizona Valentine Southeast Quadrangle, Mohave County, ern Colorado Plateau from apatite (U-Th)/He thermo- [Ph.D. dissertation]: University Park, Pennsylvania Arizona: U.S. Geological Survey Map GQ 1711, scale chronometry: Geological Society of America Bulletin, State University, 218 p. 1:24,000. v. 120, no. 5–6, p. 571–587, doi: 10 .1130 /B26231 .1 . Matmon, A., Bierman, P., and Enzel, Y., 2002, Pattern and Beard, L.S., Anderson, R.E., Block, D.L., Bohannon, R.G., Garner, H.F., 1974, The Origin of Landscapes; A Synthe- tempo of great escarpment erosion: Geology, v. 30, Brady, R.J., Castor, S.B., Duebendorfer, E.M., Faulds, sis of Geomorphology: New York, Oxford University p. 1135–1138, doi: 10 .1130 /0091 -7613 (2002)030 <1135: J.E., Felger, T.J., Howard, K.A., Kuntz, M.A., and Wil- Press, 734 p. PATOGE>2 .0 .CO;2 . liams, V.S., 2007, Preliminary Geologic Map of the Gilchrist, A.R., Kooi, H., and Beaumant, C., 1994, Post- Moore, A., and Blenkinsop, T., 2006, Scarp retreat versus Lake Mead 30′ by 60′ Quadrangle, Clarke County, Gondwana geomorphic evolution of southwestern pinned drainage divide in the formation of the Drakens- Nevada, and Mohave County, Arizona: U.S. Geo- Africa: Implications for the controls on landscape berg escarpment, southern Africa: South African Jour- logical Survey Open-File Report 2007–1010, scale development from observations and numerical experi- nal of Geology, v. 109, p. 599–610, doi:10 .2113 /gssajg 1:100,000, 3 plates and 109 p. ments: Journal of Geophysical Research, v. 99, no. B6, .109.4 .599 . Billingsley, G.H., Wenrich, K.J., Huntoon, P.W., and Young, p. 12,211–12,228, doi: 10 .1029 /94JB00046 . Persano, C., Stuart, F.M., Bishop, P., and Barfod, D.N., 2002, R.A., 1999, Breccia Pipe and Geologic Map of the Goldstrand, P.M., 1990, Stratigraphy and Paleogeography Apatite (U-Th)/He age constraints on the development Southwestern Part of the Hualapai Indian Reserva- of Late Cretaceous and Paleogene Rocks of Southwest of the Great Escarpment on the southern Australian pas- tion and Vicinity, Arizona: U.S. Geological Survey Utah: Utah Geological and Mineralogical Survey Mis- sive margin: Earth and Planetary Science Letters, v. 200, Miscellaneous Investigation Series Map I-2554, scale cellaneous Publication 90–2, 58 p. p. 79–90, doi: 10 .1016 /S0012 -821X (02)00614 -3 . 1:48,000, 2 sheets and 50 p. Goldstrand, P.M., 1992, Evolution of Late Cretaceous and Peterson, G.L., and Abbott, P.L., 1979, Mid-Eocene climatic Billingsley, G.H., Wenrich, K.J., and Huntoon, P.W., 2000, Early Tertiary basins of southwest Utah based on clas- change, southwestern California and northwestern Breccia Pipe and Geologic Map of the Southeastern tic petrology: Journal of Sedimentary Petrology, v. 62, Baja California: Palaeogeography, Palaeoclimatology, Part of the Hualapai Indian Reservation and Vicinity, no. 3, p. 495–507. Palaeoecology, v. 26, p. 73–87, doi:10 .1016 /0031 -0182 Arizona: U.S. Geological Survey Geologic Investiga- Griffi ths, P.G., Hereford, R., and Webb, R.H., 2006, Sedi- (79)90141 -X . tions Series Map I-2643, scale 1:48,000, 2 sheets and ment Yield and Runoff Frequency of Small Drainage Prince, P.S., Spotila, J.A., and Henika, W.S., 2010, New 18 p. Basins in the Mohave Desert, California and Nevada: physical evidence of the role of stream capture in active Brown, R.W., Summerfi eld, M.A., and Gleadow, A.J.W., U.S. Geological Survey Fact Sheet 2006–3007, 9 p. retreat of the Blue Ridge escarpment, southern Appa- 2002, Denudational history along a transect across the Gutierrez, M., Santo, C., and Arauzo, T., 1998, Scarp lachians: Geomorphology, v. 123, p. 305–319, doi: 10 Drakensberg Escarpment of southern Africa derived retreat rates in semiarid environments from talus fl at- .1016 /j .geomorph .2010 .07 .023 . from apatite fi ssion track thermochronology: Journal irons (Ebro Basin, NE Spain): Geomorphology, v. 25, Prothero, D.R., and Berggren, W.A., 1992, Eocene-Oligo- of Geophysical Research, v. 107, no. B12, p. 2350– p. 111–121, doi: 10 .1016 /S0169 -555X (98)00034 -8 . cene Climatic and Biotic Evolution: Princeton, New 2368, doi:10 .1029 /2001JB000745 . Huntoon, P.W., 1981, Grand Canyon monoclines: Verti- Jersey, Princeton University Press, 566 p. Chorley, R.J., Schumm, S.A., and Sugden, D.E., 1984, Geo- cal uplift or horizontal compression?, in Boyd, D.W., Schmidt, K.-H., 1989, The signifi cance of scarp retreat for morphology: London, Methuen & Co., Ltd., 605 p. and Lillegraven, J.A., eds., Rocky Mountain Fore- Cenozoic landform evolution on the Colorado Plateau,

678 Geosphere, August 2014

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021 Paleogene Grand Canyon unlikely

U.S.A.: Earth Surface Processes and Landforms, v. 14, Plateau: Tectonophysics, v. 61, p. 25–47, doi: 10 .1016 Young, R.A., 2008, Pre–Colorado River drainage in west- p. 93–105, doi: 10 .1002 /esp .3290140202 . /0040 -1951 (79)90290 -7 . ern Grand Canyon: Potential infl uence on Miocene Spencer, J.E., and Reynolds, S.J., 1989, Middle Tertiary tec- Young, R.A., 1982, Paleogeomorphologic evidence for the stratigraphy in Grand Wash Trough, in Reheis, M.C., tonics of Arizona and adjacent areas, in Jenny, J.P., and structural history of the Colorado Plateau margin in Hershler, R., and Miller, D.M., eds., Late Cenozoic Reynolds, S.J., eds., Geologic Evolution of Arizona: Arizona, in Frost, E.G., and Martin, D.L., eds., Meso- Drainage History of the Southwestern Great Basin and Arizona Geological Society Digest, v. 17, p. 539–574. zoic-Cenozoic Tectonic Evolution of the Colorado Lower Colorado River Region: Geologic and Biotic Steckler, M.S., and Omar, G.I., 1994, Controls on ero- River Region, California, Arizona, and Nevada: San Perspectives: Geological Society of America Special sional retreat of the uplifted rift fl anks at the Gulf of Diego, Cordilleran Publishers, p. 29–39. Paper 439, p. 319–333. Suez and northern Red Sea: Journal of Geophysical Young, R.A., 1985, Geomorphic evolution of the Colorado Young, R.A., 2011, Brief Cenozoic Geologic History of the Research, v. 99, no. B6, p. 12,159–12,173, doi: 10 .1029 Plateau margin in west-central Arizona: A tectonic Peach Springs Quadrangle and the Hualapai Plateau, /94JB00278 . model to distinguish between the causes of rapid sym- Mohave County, Arizona (Hualapai Indian Reserva- Steiger, R.H., and Jager, E., 1977, Subcommission on geo- metrical scarp retreat and scarp dissection, in Hack, tion): Arizona Geological Survey Contributed Report chronology: Convention on the use of decay constants J.T., and Morisawa, M., eds., Tectonic Geomorphol- CR-11-O, 28 p., map scale 1:24,000, cross section. in geochronology and cosmochronology: Earth and ogy: London, Allen and Unwin, p. 261–278. http:// repository .azgs .az .gov /uri _gin /azgs /dlio /1362. Planetary Science Letters, v. 36, p. 359–362. Young, R.A., 1989a, Paleogene-Neogene deposits of western Young, R.A., and Hartman, J.H., 2011, Early Cenozoic Taylor, J.R., 1982, An Introduction to Error Analysis: The Grand Canyon, Arizona, in Elston, D.P., Billingsley, “Rim Gravel” of Arizona—Age, distribution and geo- Study of Uncertainties in Physical Measurements: Mill G.H., and Young, R.A., eds., Geology of Grand Canyon, logic signifi cance, in Beard, L.S., Karlstrom, K.E., Valley, California, University Science Books, 270 p. Northern Arizona: Washington, D.C., American Geo- Young, R.A., and Billingsley, G.H., eds., CREvolu- Twenter, F.R., 1962, Geology and Promising Areas for physical Union, 28th International Geological Congress tion 2—Origin and Evolution of the Colorado River Groundwater Development in the Hualapai Indian Fieldtrip Guidebook T115/315, p. 166–173. System, Workshop Abstracts: U.S. Geological Survey Reservation, Arizona: U.S. Geological Survey Water- Young, R.A., 1989b, Late Cretaceous–Paleocene paleod- Open-File Report 2011–1210, p. 274–286. Supply Paper 1576-A. 38 p. rainage system of western Grand Canyon: Evidence Young, R.A., and Hartman, J.H., 2014, Paleogene “Rim Wenrich, K.J., Billingsley, G.H., and Blackerby, B.A., for structural controls, in 28th International Geological Gravel” of Arizona: Age and signifi cance of the 1995, Spatial migration and compositional changes of Congress Abstracts: Washington, D.C., American Geo- Music Mountain Formation: Geosphere, doi:10 .1130 Miocene-Quaternary magmatism in the western Grand physical Union, v. 3, p. 3-415–3-416. /GES00971 .1 (in press). Canyon: Journal of Geophysical Research, v. 100, Young, R.A., 1999, Nomenclature and ages of Late Creta- Young, R.A., and Huntoon, P.W., 1987, Laramide canyon no. B7, p. 10,417–10,444, doi: 10 .1029 /95JB00373 . ceous(?)–Tertiary strata in the Hualapai Plateau region, remnants along the Hurricane fault zone: Tectonic Wenrich, K.J., Billingsley, G.H., and Huntoon, P.W., 1996, northwest Arizona, in Billingsley, G.H., Wenrich, K.J., disruption by monoclinal folding: Geological Soci- Breccia Pipe and Geologic Map of the Northwestern Huntoon, P.W., and Young, R.A., eds., Breccia Pipe and ety of America Abstracts with Programs, v. 19, no. 7, Part of the Hualapai Indian Reservation and Vicinity, Geologic Map of the Southwestern Part of the Hualapai p. 903. Arizona: U.S. Geological Survey Geologic Investiga- Indian Reservation and Vicinity, Arizona: U.S. Geo- Young, R.A., and McKee, E.H., 1978, Early and middle tions Series Map I-2522, scale 1:48,000, 2 sheets and logical Survey Miscellaneous Investigations Series Map Cenozoic drainage and erosion in west-central Ari- 16 p. I-2554, scale 1:48,000, 2 sheets, Appendix, p. 21–50. zona: Geological Society of America Bulletin, v. 89, Wernicke, B., 2011, The California River and its role in Young, R.A., 2001a, Geomorphic, structural, and strati- p. 1745–1750, doi: 10 .1130 /0016 -7606 (1978)89 <1745: carving Grand Canyon: Geological Society of America graphic evidence for Laramide uplift of the southwest- EAMCDA>2 .0 .CO;2 . Bulletin, v. 123, p. 1288–1316, doi: 10 .1130 /B30274 .1 . ern Colorado Plateau margin in northwestern Arizona, in Young, R.A., Crow, R., and Peters, L., 2011, Oligocene tuff Young, R.A., 1966, Cenozoic Geology along the Edge of Erskine, M.C., Faulds, J.E., Bartley, J.M., and Rowley, corroborates older Paleocene–Eocene age of Hualapai the Colorado Plateau in Northwestern Arizona [Ph.D. P.D., eds., The Geologic Transition Colorado Plateau Plateau basal Tertiary section, in Beard, L.S., Karl- thesis]: St. Louis, Missouri, Washington University, to Great Basin—A Symposium and Field Guide (The strom, K.E., Young, R.A., and Billingsley, G.H., eds., 167 p. Mackin Volume): Utah Geological Association Publica- CREvolution 2—Origin and Evolution of the Colorado Young, R.A., 1970, Geomorphological implications of tion 30, p. 227–237. River System, Workshop Abstracts: U.S. Geological pre-Colorado and Colorado tributary drainage in the Young, R.A., 2001b, The Laramide-Paleogene history of Survey Open-File Report 2011–1210, p. 267–273. western Grand Canyon region: Plateau, v. 42, no. 3, the western Grand Canyon region: Setting the stage, in Young, R.W., and Wray, R.A.L., 2000, Contribution to the p. 107–117. Young, R.A., and Spamer, E.E., eds., Colorado River, theory of scarpland development from observations in Young, R.A., 1979, Laramide deformation, erosion and plu- Origin and Evolution: Grand Canyon Association central Queensland, Australia: The Journal of Geology, tonism along the southwestern margin of the Colorado Monograph 12, p. 7–15. v. 108, p. 705–719, doi: 10 .1086 /317949 .

Geosphere, August 2014 679

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/4/664/3332772/664.pdf by guest on 28 September 2021