Downloaded from gsabulletin.gsapubs.org on January 23, 2013 Geological Society of America Bulletin

Early History of the Colorado River in the Basin and Range Province

IVO LUCCHITTA

Geological Society of America Bulletin 1972;83, no. 7;1933-1948 doi: 10.1130/0016-7606(1972)83[1933:EHOTCR]2.0.CO;2

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Notes

Copyright © 1972, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. Downloaded from gsabulletin.gsapubs.org on January 23, 2013

IVO LUCCHITTA U.S. Geological Survey, Center of Astrogeology, 601 E. Cedar Ave., Flagstaff, Arizona 86001

Early History of the Colorado River in the

Basin and Range Province

ABSTRACT 18 to 20 m.y. indicate drainage northward, across the present site of Lake Mead, and A reasonable interpretation of the geologic northeastward onto the Colorado Plateau. history of the Colorado River in the Basin and None of these drainages can be interpreted as Range province can be put together by con- being an ancestral Colorado River. The next sidering the work done by several geologists in youngest deposit is the Muddy Creek Forma- the Imperial Valley, California, the Parker- tion, which was laid down in interior basins Blythe-Cibola area, California and Arizona, formed when basin-range faulting disrupted the and, the Lake Mead and Hualapai Plateau older topography and drainage some time after areas, Arizona. 18 to 20 m.y. ago. There was no Colorado River In the Imperial Valley, the Imperial Forma- at this time. Deposition of the Muddy Creek tion, whose age has been interpreted variously Formation ended some time after 10.6 m.y. as late Miocene or early Pleistocene but most ago. Younger deposits reflect the Colorado commonly Pliocene, records a transgression of River which, by 3.3 m.y. ago, was a well- the marine waters of the Gulf of California and incised stream flowing within 350 ft of its deposition of sediments very probably of present grade. Colorado River origin. These sediments contain Deposits and erosion surfaces on the Hualapai reworked Late Cretaceous foraminifers derived Plateau reflect drainage northeastward onto from the Mancos Shale of the Colorado the region of the present plateau from the Basin Plateau. Later sediments record a gradual and Range province until about 18 m.y. ago, change from marine to continental conditions. when the two provinces became separated In the Parker-Blythe-Cibola area, extend- topographically by movements along the ing along the Colorado River, the Bouse Grand Wash fault. No Colorado River existed Formation (Metzger, 1968), of Pliocene age, before the faulting. After faulting, drainage records a marine transgression in the form of an became interior. In none of the areas is there embayment of the Gulf of California. A evidence to suggest that the Colorado River possible northward decrease in salinity, evi- has departed appreciably from its present denced by faunas in the Bouse Formation, and course. a volume of sediments too large to be ac- This information leads to the following hy- counted for by local sources, suggest that a pothesis: until about 10.6 m.y. ago, or shortly large river emptied into the Bouse embayment thereafter, there was no Colorado River. After from the north. Although other streams and that date, waters of the Gulf of California in- washes may have contributed sediments to the vaded the Bouse embayment, and the ancestral embayment, it is probable that the main source Colorado River became established in the Lake was the ancestral Colorado River. The Bouse Mead area. The river emptied into the embay- Formation does not contain Mancos-type ment, which it progressively filled with its sedi- foraminifers but, in some surface exposures, ments from north to south. At this time, the does include Late Cretaceous coccoliths, head of the river had not yet reached areas probably of relatively local derivation. Depos- where the Mancos Shale cropped out (probably its younger than those of the Bouse Formation east of the Kaibab upwarp). As the sediment consist of Colorado River alluvium generally fill continued to build toward and into the unconformable on the Bouse, but locally con- Imperial Valley area, the headwaters of the formable. river breached the uplift and reached the In the Lake Mead area, deposits as young as Mancos Shale. The sediments then continued

Geological Society of America Bulletin, v. 83, p. 1933-1948, 3 figs., July 1972 1933 Downloaded from gsabulletin.gsapubs.org on January 23, 2013 1934 I. LUCCHITTA

to build southward, rilling the head of the Gulf tions between the various areas, and points out of California, a process still going on. By 3.3 problems still unsolved. In addition, this in- m.y. ago, the river was a well-established formation supports a hypothesis that, though stream in the Lake Mead area, where it had highly tentative, can nevertheless provide a cut to within a few hundred feet of its present context for further research. This hypothesis is grade. controversial. I present it in the deliberate hope By this interpretation neither the Bouse that it will stimulate productive discussion of Formation nor the part of the Imperial Forma- the problem and perhaps bring out important tion containing Colorado River material is information not now generally available. This older than 10.6 m.y. If true, the Bouse Forma- paper does not attempt to be an exhaustive tion is in part older than and in part equivalent treatment of the subject, and many questions in time to the Imperial Formation. are touched on lightly or not at all. Some of these questions will be discussed in a paper INTRODUCTION being prepared by Lucchitta and Young. The origin, age, and history of the Colorado Others are treated in syntheses such as those River have long been of interest to geologists, of McKee and others (1967), and C. B. Hunt partly because unusual conditions must have (1969), which provide a broad perspective and existed to produce the Grand Canyon, and points of view in part alternative to that partly because great difficulties are encountered presented here. in explaining how the river could establish a The four areas considered in this report are course so independent of the major topographic (Fig. 1): Imperial Valley; Parker-Blythe- and structural features that lie across its path. Cibola area; Lake Mead area; and the Hualapai Probably the most impressive of these features, Plateau. Of these, I am personally acquainted and the one that raises most problems in un- with the last two, especially the Lake Mead derstanding the history of the river, is the area. Information for the other areas has been Kaibab upwarp, a structural and topographic obtained from the literature and from com- high trending approximately north, directly munication with geologists who have experi- athwart the general course of the river at the ence with these areas. eastern, or upstream, end of the Grand Canyon. Largely because of this, recent work IMPERIAL VALLEY AREA on the history of the Colorado River often This synthesis is made chiefly from the considers this upwarp as the dividing line be- papers of Allison (1964), Dibblee (1954), tween an upper and lower section of the Durham (1950), Durham and Allison (I960), Colorado River, and therefore tends to treat Merriam and Bandy (1965), and Muffler and the two sections individually, subsequently Doe (1968). Additional information is obtained attempting to tie them together across the from Smith (1970) and Bukry (1969, 1970, upwarp. written commun.). The scope of the present paper is restricted The Imperial Valley is in the Salton Trough, to the section of the Colorado downstream of a tectonic feature consisting of the northwest or the Kaibab upwarp, specifically from near the landward extension of the Gulf of California mouth of the Grand Canyon to about 100 mi structural depression. The valley is traversed upstream from the mouth of the river. Its at its southeastern end by the Colorado River, purpose is to summarize and tie together re- which in that area is about 100 mi upstream sults obtained by various geologists from key from its mouth. The highlands bordering the areas in this section. Although this part of the valley reach altitudes of 6,000 ft in the Penin- river is largely in the Basin and Range province, sular Range to the west. The San Andreas fault it has a profound influence on interpretations zone runs along the eastern margin of the valley of the history of the Grand Canyon and indeed (Fig- 1). of the river as a whole. The Cenozoic fill of the valley, as much as Information currently available is frag- 20,000 ft thick, can be subdivided into two mentary, obtained from widely scattered groups: (1) coarse sediments of local derivation sources, and in some instances rather con- at the margins of the valley, grading basinward troversial. Nevertheless, it should be brought into (2) fine-grained sediments, at least in part together to provide a frame of reference that of distant derivation. The deposits and their underscores key information, clarifies the rela- mutual relations are shown in Figure 2. Downloaded from gsabulletin.gsapubs.org on January 23, 2013 EARLY HISTORY OF COLORADO RIVER 1935

NEVADA

Las Vegas Hoover Dam

Colored o Plateau

C ALIFORNIA San Andreas fault

B A J A C A LIFORNI

75miles I Figure 1. Location map. The Imperial Formation consists of marine ment content of the Imperial Formation with fine grained sandstone, siltstone, and claystone; similar parameters for undoubted Colorado younger deposits are nonmarine. The Imperial River sediments (recent delta, delta in Lake Formation also marks the lowest horizon at Mead from Merriam and Bandy, 1965; recent which far-traveled material of postulated deltaic sediments in the Salton Basin from Colorado River origin is present. This origin is Muffler and Doe, 1968). As a similar origin inferred by comparing grain size, mineral com- applies to the fine-grained material overlying position, chemical composition, and trace ele- the Imperial Formation, according to Muffler Downloaded from gsabulletin.gsapubs.org on January 23, 2013 1936 I. LUCCHITTA

SYSTEM SERIES FORMATION HOLOCENE Sand,silt,and clay (subaerial) rr UJ Brawley Fm. z UJ (lacustrine) a: o o Borrego Fm. (lacustrine) UJ o _i a Palm Spring Fm. _ o (Mostly subaerial. Subordinate LJ and temporary marine Z incursions.) <; ^x^xj .••••,•• •.:::•*••,• LU xXxCane bra k.e:::x: C.g.l.: O O Imperial Fm. (marine) rr

LJ tr. z Fish Creek Gypsum u LJ (playa deposit) O O : : : : : : : : :X: : :'.confllpmer9te.,brecci9.K:::::x

PRE-TERTIARY Igneous and metamorphic rocks

Figure 2. Generalized stratigraphy of the Salton See text for disagreement on the age of Imperial trough. From Muffler and Doe (1968, Fig. 2). This Formation. Coarser grained deposits are shown as figure is presented here to show stratigraphic relations. screen pattern. and Doe (1968), the entire fine-grained section mostly Pliocene to Holocene, but that is as- above and including the Imperial consists sociated with a puzzling abundance of Bolivina essentially of deltaic deposits of the Colorado guadalupae Parker, characteristic of the middle River. and late Miocene of California. Late Cretaceous foraminifers similar in type Whereas the Late Cretaceous coccoliths are and mode of preservation to those ol the present in rocks cropping out near the Imperial Mancos Shale of the Colorado Plateau have Valley (for example, the Penisular Range) and been reported from the Imperial and younger could thus be of relatively local derivation, the formations by Merriam and Bandy (1965) and Late Cretaceous foraminifers must be reworked by Allison (1969, written commun.), who because they are found only in the Mancos found them associated with Late Cretaceous Shale of the Colorado Plateau and not locally. coccoliths. According to Bukry (1970, written The Miocene and Pliocene toraminifers lived in commun.), these coccoliths are also found in the Imperial Sea, which may have extended as the Imperial Formation of the Coyote Moun- far north as the present Danby and Cadiz dry tains (Fig. 1); this flora is similar to the less lakes (Durham and Allison, 1960). abundant one taken from the Bouse Forma- The age and correlation of the Imperial tion (see below) along the Colorado River. Formation are controversial. Earlier reports According to Smith (letter to Bukry, 1968) the placed the formation in the late Miocene or Coyote Mountains material also contains a early Pliocene, but in the more recent view it shallow marine foraminiferal fauna that is generally is considerably younger. Thus, Dib- Downloaded from gsabulletin.gsapubs.org on January 23, 2013 EARLY HISTORY OF COLORADO RIVER 1937 blee (1954) considers the formation of "upper obtained elsewhere along the Colorado River Miocene or possibly lower Pliocene age"; Dur- (see below). ham (1950), early Pliocene; Merriam and Whatever the exact age of the Imperial For- Bandy (1965, p. 913), late Miocene for some mation, in Imperial time a large river carried sections, but younger, perhaps Pliocene, for material similar to that of the Colorado River others; Muffler and Doe (1968), late Miocene into the sea occupying the general area of the to Pliocene (after Dibblee, 1954 and Merriam present Salton Trough. and Bandy, 1965). Bandy now considers the Imperial Formation younger than 6 or 7 m.y. Parker-Blythe-Cibola Area (1968, written commun.), whereas Allison Deposits present in and near the valley of (1969, written commun.) stated that "most the Colorado River from near Yuma to as far Imperial faunas seem to be close to the Pleisto- north as Davis Dam (Metzger, 1969, oral com- cene-Pliocene boundary or above." Allison mun.) have been studied by Metzger (1968), however, did not discount the possibility of who has named them the Bouse Formation. finding rocks of Imperial Formation type with Smith (1970) has studied the fauna of the Miocene fossils (1968, written commun.). On Bouse and made paleoecologic interpretations. the other hand, Wendell Woodring considers it The information presented below is from late Miocene or early Pliocene (1971, oral Metzger's 1968 paper except where otherwise commun.), and Louis J. Simon feels that it is indicated. Miocene (Patsy Smith, 1970, oral commun.). The Bouse Formation is exposed as scattered The foraminifers described by Smith (see erosional remnants attaining a maximum thick- above) indicate a Pliocene to Holocene age, ness of 215 ft. In the subsurface it is present except for the common Bolivina guadalupae throughout the area and attains a maximum Parker, which points to a late Miocene age for known thickness of 767 ft; the maximum actual at least part of the formation. thickness maybe considerably greater. Metzger The problem of the age and correlation of the recognizes three units: (1) basal limestone, Imperial Formation was summarized by Allison overlain by (2) interbedded clay, silt, and (1964), who stated that a correlation between sand, mostly evenly bedded but with local much of the Imperial and the San Diego For- crossbedding in the sand layers; both con- mation of Southern California is suggested by temporaneous with (3) tufa that was being the presence of the warm-water echinoid, En- deposited against topographic highs formed by cope tenuis Kew in both formations, which in- older rocks. The Bouse rests unconformably on dicates a Pliocene age. Furthermore, strata a Miocene (?) fanglomerate of local derivation with the oldest recognized Imperial Formation and is generally overlain by Colorado River faunas near San Felipe, Baja California, are alluvium resting on an erosiona) surface. Near underlain unconformably by marine diatomite Yuma, however, the Bouse grades upward into, and mudstone of late Miocene age, which have and interfingers with, the Colorado alluvium as yet failed to produce the reworked Upper (Metzger, 1969, oral commun.). Cretaceous microfossils common in the Imper- Fossils are common in the Bouse Formation, ial Formation (Allison, 1969, written com- but the number of species is small. Represented mun.). The Imperial Formation would thus are foraminifers, mollusks, ostracodes, charo- seem to be mostly younger than late Miocene phytes, and barnacles. The fossils, though not and probably of Pliocene age. But if the adequate to assign an age, show that the en- boundary between the Pliocene and the vironment of deposition was brackish water and Pleistocene is to be drawn at the base of the suggest that this environment was progressively marine Calabrian and nonmarine Villafranchian fresher to the north. Smith (1970) admits the stages as decided by the 1948 International presence of brackish water, but denies the Geological Congress, the San Diego and, by existence of definite trends in salinity. Her correlation, the Imperial would be more likely data, however, are not incompatible with the Pleistocene than Pliocene in age (Allison, 1964). near-estuarine environment and with the north- These uncertainties, which probably stem from ward decrease in salinity postulated by Metz- the Imperial being a unit that includes rocks of ger. No Mancos-type foraminifers similar to different ages in different places, compound the those in the Imperial Formation have been difficulties encountered in placing the Imperial found, but identical coccoliths have been ob- Formation in context with radiometric dates tained from the surficial exposures of the Bouse Downloaded from gsabulletin.gsapubs.org on January 23, 2013 1938 I. LUCCHITTA

though not from subsurface rocks (Patsy B. with a course probably similar to that of the Smith, 1969, written commun.). Metzger feels present Colorado River, very likely was the that the stratigraphic level of these coccolith- ancestral Colorado. At least, no evidence of bearing rocks is not known at this time (Metz- other major rivers with a different course has ger, 1968, oral commun.). yet been found in the Parker-Blythe-Cibola The nondevitrified fraction of a tuff layer area, although sediments may have been con- near the base of the Bouse Formation has tributed by washes heading in the Great Basin. yielded K/Ar ages of 5.4 + 0.2 m.y. (Damon, Other rivers may have existed to the south and 1972, oral commun.) and 8.1 + 0.5 m.y. east, near the present Gila and Salt Rivers. (Damon, 1970). Damon (1972, oral commun.) Additional information on the source of the considers the 5.4 m.y. date to be the most Bouse Formation can be obtained from a com- reliable. An earlier determination on the same parison of Bouse sediments with those of the tuff but without separation of the nondevitri- modern Colorado, as was done for the Imperial fied material yielded an age of 3.02 + 1.15 Formation. m.y. (Damon, 1968). This represents a mini- mum age for the tuff. Vertebrate fossils of LAKE MEAD AREA middle Miocene age are found in steeply The Lake Mead area, described by Longwell dipping beds in the Sacramento Mountains (1936, 1946, 1963) and more recently by Luc- west of Needles, California. Similar beds occur chitta (1966), provides key information on south of Needles, where they are overlain un- conditions existing both before and after estab- conformably by Miocene (?) fanglomerate lishment of the Colorado Plateau and the Basin which, in turn, is overlain by the Bouse. The and Range province.1 Bouse therefore, cannot be older than middle The Colorado River leaves the plateau and Miocene (Metzger, 1970, written commun.). the Grand Canyon at the Grand Wash Cliffs, a Metzger feels that the formation can be as- north-trending fault scarp. Thence, the west- signed safely to the Pliocene. Smith (1970) erly course of the river cuts across north-trend- states that the Yuma section and, by inference, ing fault-block ranges and intervening basins the Parker-Blythe-Cibola section are post- that are typical of the Basin and Range prov- Miocene, and probably Pliocene. ince. The basins are filled by the Muddy Creek According to Metzger, Bouse-like deposits Formation, a typical interior basin deposit. extend into the Chuckwalla Valley, possibly The Muddy Creek rests unconformably on all into the Cadiz and Danby dry lakes (which older rocks, and is overlain unconformably by deposits may also correlate with the Imperial Colorado River deposits. The Muddy Creek Formation, see above) northward to Cotton- Formation is much less deformed than older wood Valley north of Davis Dam, along the rocks. Fossils in the Muddy Creek are scarce, lower Gila River, and into the Salt River poorly preserved, and of little diagnostic value Valley west of Phoenix, Arizona. for age assignment. At Fortification Hill (Fig. It would appear, then, that in Bouse time, 1), a sequence of lava flows, the type Fortifica- about 5 m.y. ago, an embayment of the Gulf of tion Basalt Member, occurs high within the California extended into the Parker-Blythe- Muddy Creek section. Their smooth and con- Cibola area as well as some of the surrounding formable basal contact is interpreted by Long- country, and probably reached as far north as well as a surface aggradation (Longwell, 1936). Davis Dam. A large river emptied into this 1 As this paper went to press, Anderson and others embayment, as shown by the decreased salinity (1972) published an article giving new radiometric ages in the embayment and by the volume of Bouse and geologic interpretations for Tertiary rocks in the sediments, which Metzger considers too great western Lake Mead region. These results are not in- to be accounted for solely by erosion of local corporated in this paper. Although their ages for the highlands. That this river emptied into the Muddy Creek and the Horse Spring Formations include embayment from the north is suggested by the values younger than those given here, no serious dif- apparent decrease in salinity from south to ficulty arises with the interpretations presented herein. It should be noted that Anderson and others (1972) have north, by the distribution of the Bouse Forma- expanded the definition of the Fortification Basalt tion along the present valley of the Colorado Member of the Muddy Creek Formation to include River in the Parker-Blythe-Cibola area, and rocks from various localities and stratigraphic positions, by the fact that the north was generally the whereas the term, as used here, refers specifically to the landward side of the embayment. Such a river, lavas capping Fortification Hill. Downloaded from gsabulletin.gsapubs.org on January 23, 2013 EARLY HISTORY OF COLORADO RIVER 1939

The flows have been dated by Damon (1965) at indicated by a thickening and coarsening in 10.6 ± 1.1 m.y. Before filling of Lake Mead, that direction by the bevelling of progressively similar lava flows, correlated by Longwell with older rocks to the south, and by the inclusion those of Fortification Hill, were exposed within of igneous and metamorphic material which can the Muddy Creek section near the mouth of only have been derived from the Precambrian Las Vegas Wash, 3 to 4 mi northwest of Forti- terrane south of the lake, where the Pre- fication Hill. No thickness is given by Long- cambrian is directly overlain by Tertiary vol- well for the section above the lava, but judging canic rocks and Tertiary and Quaternary basin by his cross-section for the area (Longwell, fill and alluvium. This terrane, which occupies 1936, PI. 2), the thickness is not great. The much of western Mohave County, Arizona, top of the section appears to be erosional. The must have been a topographic high and a correlation, if correct, indicates that the Forti- source of sediments for most of the Cenozoic fication Basalt Member is not the youngest and part of the Cretaceous. part of the Muddy Creek Formation and that All available evidence thus suggests that in Muddy Creek deposition continued until some pre-Muddy Creek time, drainage was generally unknown time after 10.6 m.y. ago. Edwin H. to the north and northeast, a direction quite McKee (1971, oral commun.) has obtained a different from that of the present Colorado whole-rock K/Ar age of 10.6 m.y. on basalt River. It is unlikely that a Colorado River with (not the Fortification Member) in the Muddy a course at all similar to its present one existed Creek Formation. The youngest pre-Muddy in pre-Muddy Creek time in the area west of Creek deposit in the Lake Mead area is the the Hualapai Plateau, especially since this hy- Horse Spring Formation, which crops out north pothesis implies that the drainage would have of the lake. Various K/Ar dates on the Horse survived an intense episode of basin and range Spring cluster around 20 m.y. (Tschanz, 1960; tectonism that completely changed the geog- Armstrong, 1963; Damon, 1965). The Muddy raphy of the region. Creek Formation is thus younger than about 20 No evidence for an ancestral Colorado River m.y. and mostly older than 10.6 m.y. The dates debouching from the Colorado Plateau in obtained from the upper part of the Muddy Muddy Creek time, as suggested by Lovejoy Creek Formation are near the Miocene-Plio- (1969), is present in Muddy Creek deposits cene boundary. Considering that the Muddy of the Grand Wash trough. Instead, these Creek is the fill of structural troughs formed by deposits reflect a typical interior basin en- basin and range faulting, and that some de- vironment with the bulk of the material formation of this kind had already occurred by coming from west and north. Short and steep about 18 m.y. ago, as documented for the canyons of Muddy Creek age are present in the Grand Wash fault (see below), it seems likely Grand Wash Cliffs. These canyons are choked that deposition of the Muddy Creek Formation by coarse and angular Muddy Creek debris of began in the Miocene and continued into the local derivation; the associated fans are also Pliocene. locally derived. These rocks grade basinward The Horse Spring Formation consists of into fine-grained material. At the mouth of the lacustrine deposits, with minor admixtures of Grand Canyon, one can find neither the fluvial material. As it is cut and tilted by the remnants of a large ancient canyon nor the far- basin-range faulting, it predates the faulting. traveled Muddy Creek material that one At the outcrop scale, the formation is, in many should find at that location had a Colorado places, structurally conformable with older River of that age existed. There are indeed rocks, from which it is separated by an erosion remnants of a Muddy Creek fan near the mouth surface of low relief. Regionally, however, the of the Grand Canyon, but the material making base of the formation truncates older rocks up the fan is all locally derived, and the struc- and rests on successively older units toward ture reflects a steep and short canyon, rather the south. These characteristics indicate a than the large canyon of a through-flowing source area toward the south. master stream. Cretaceous and sedimentary rocks older than In places, the highest and youngest member the Horse Spring Formation are restricted to of the Muddy Creek Formation is the Hualapai the area north and northwest of Lake Mead. Limestone, a fresh-water deposit locally as According to Longwell and others (1965), a much as 1,000 ft thick. Hunt (1969) considers southerly provenance for some of these rocks is the limestone to have been deposited in a large Downloaded from gsabulletin.gsapubs.org on January 23, 2013 1940 I. LUCCHITTA

deep lake, centered near the mouth of the Muddy Creek deposits are widely distributed Grand Canyon. The lack of clastic material in in the entire Lake Mead region as well as in the limestone suggests to him that no large other adjoining basins, indicating that con- stream emptied into the lake. Yet a large lake ditions of interior drainage were general rather needs to be maintained against evaporation. than local. Hunt solves the problem by invoking large- The oldest datable deposits of the Colorado scale piping of water from the ancestral Colo- River in the Lake Mead area are cemented rado River, at that time supposedly dammed in river gravel cropping out in various localities Peach Springs Canyon (Fig. 1), to the Hualapai along the course of the river. Before filling of Lake which was located where the mouth of the lake, many of these remnants could be seen the Grand Canyon is now. According to Hunt at or near river level (Longwell, 1936); one of (1969, p. 113) this hypothesis is reinforced by the more conspicuous remnants preserved the presence of an unconformity between the above the waters of the lake is at Sandy Point limestone and the underlying Muddy Creek (Fig. 1), where the base of the gravels is about rocks, which would make the limestone younger 350 ft above river grade. According to Long- than the Muddy Creek and perhaps nearly as well (1936), the base of another remnant less young as the oldest Colorado River gravels. than one mile away from Sandy Point was only The problems involved in routing an ancestral 150 ft above river grade. The basalt flow in- Colorado River through Peach Springs Canyon cluded in the remnant at Sandy Point has been are discussed later in this paper. Other aspects dated at 3.3 ± 0.4 m.y. (Damon, 1972, oral of Hunt's hypothesis do not appear consonant commun.), showing that the Colorado River is with the following data, obtained by Lucchitta at least that old. In fact, the river is probably (1966) in a detailed study of the upper Lake considerably older, as the time required for the Mead area: river to cut its valley to almost the present 1. The Hualapai Limestone is not centered depth must be added to the age indicated by about the mouth of the Grand Canyon, but the lava. rather extends more than 20 mi southwestward In summary, the Colorado River in its from that point. As exposures preserved are present course through the Lake Mead area is erosional remnants, the original extent of the at most 10.6 m.y. old (earliest Pliocene), prob- limestone probably was even greater. Erosional ably somewhat less. And as the river had cut remnants in widely scattered localities are as down to near its present depth by 3.3 m.y. impressive as those near the mouth of the ago, it was by that time (late Pliocene) a well- canyon. established river flowing in a deeply incised 2. The limestone was not laid down in one channel. And as the Grand Canyon debouches lake. At least two lakes can be documented in directly into the Lake Mead country, these the upper Lake Mead area; these lakes prob- age limits hold for the Grand Canyon as well, ably were not connected, and occupied basins or at least for its western part. with independent tectonic and geomorphic histories. The same may well hold for areas HUALAPAIPLATEAU farther west, which were also tectonically The Hualapai Plateau has been studied active. recently by Young (1966a, 1970), from whom 3. The limestone was not laid down in a deep most of the following information was obtained. lake. The distribution of facies in the old basins, The plateau is the westernmost part of the and internal characteristics of the Hualapai Colorado Plateaus province directly south of Limestone, such as plant stem impressions and the Grand Canyon. Its western margin is the interbedded evaporites, all point to a classic scarp of the Grand Wash Cliffs, which separates interior basin in which the topographically it from the Basin and Range province and the lowest part is occupied by playas and shallow Lake Mead region to the west. lakes rich in salts, both of which become more The Hualapai Plateau consists of an erosion extensive as the basin is filled, relief reduced, surface that slopes gently northeast and is cut and the contributions of coarse-grained detrital into Paleozoic rocks dipping a few degrees in material from surrounding highlands decrease. the same direction and, locally, into Precam- No evidence is present for a large stream brian rocks. The rocks dip more steeply than emptying into the lakes, either directly or by the surface, so that progressively younger rocks means of large-scale piping. are exposed to the northeast. The surface is Downloaded from gsabulletin.gsapubs.org on January 23, 2013 EARLY HISTORY OF COLORADO RIVER 1941

WILLOW SPRINGS FM. Limestone conglomerate Mainly Pliocene I 0-300' (Local derivation)

18.3 ± 0.6 m.y.

BUCK AND DOE CONGLOMERATE Limestone conglomerate 0-150 Red siltstone and claystone 0—30 •WESTWATER FM. Fresh-water limestone 0-45'

HINDU r-ANbLUMtKAFANGLOMERATi Et Found against canyon walls over an elevation range of 400

Figure 3. Diagrammatic section of Cenozoic units. Nomenclature is that of Young (1966a, 1966b, deposits on the western part of the Hualapai Plateau, 1970). Units of distant derivation are shown as screen showing composite thicknesses and relationship of pattern. older than the Colorado River, which dissects distributed over the erosion surface mentioned it, and also older than the Grand Wash Cliffs, earlier. The flows and the tuff have a south- which truncate it. The surface thus predates westerly derivation, from the present Basin faulting along the Grand Wash Cliffs, and dates and Range province, and are cut by the Grand back to the time when the Colorado Plateau Wash fault. The tuff (Fig. 3), the Peach Springs and the Basin and Range province were not dif- Tuff of Young (1966b), has yielded a radio- ferentiated in the area and the plateau was metric age of 18.3 + 0.6 m.y. Deposits younger topographically and structurally low. Channels than the flows and the tuff, and probably of that also trend northeast are incised into the Pliocene age, reflect conditions of local and erosion surface and are beheaded by the Grand interior drainage. Wash fault. The channels contain old gravel The arkosic gravel beds in the old channels beds that are in part arkosic and thus could can be traced to a point in Peach Springs have come only from Precambrian rocks in the Canyon now at an altitude of about 3,300 ft. present Basin and Range province to the west No satisfactory continuation has yet been and southwest. This provenance is supported found. Hunt (1969) suggests that the old chan- by directions of imbrication. The intercalation nels were tributary to the ancestral Colorado of far-travelled arkosic gravels with gravels of River, at that time flowing southwestward local derivation indicates repeated and tem- through Peach Springs Canyon-Truxton Wash porary interruptions of drainage, probably by (Fig. 1), and thence to a gap near Kingman. early movements on the Grand Wash fault to However: (1) no distinctive Colorado River the southwest. The gravels in the channels are gravels have been found in the old gravel beds overlain by other gravel beds, lava flows, and a in Peach Springs Canyon or in the gap near welded tuff (Fig. 3), all of which are widely Kingman, (2) the bedrock floor of Truxton Downloaded from gsabulletin.gsapubs.org on January 23, 2013 1942 I. LUCCHITTA

Valley probably slopes northeast, and (3) the Hualapai Plateau, the drainage predating gravels, lavas, and the Peach Springs Tuff the episode of interior basin deposition was so reflect a regional slope to the northeast, op- different from that of the present Colorado posite to that the postulated drainage. More that it can scarcely be related to it. One can likely, the old drainage continued northward tentatively conclude that the Colorado River from Peach Springs Canyon into a relatively contributed the bulk of the material in ques- low area located north of the Colorado River tion that is of fluvial origin and of post-Muddy and about 40 mi away. Although this area is Creek age; that the river during its known now 2,000 to 3,000 ft higher than the lowest history has followed approximately its present gravel beds in Peach Springs Canyon, the course in the Basin and Range province; and slope represented is only .5 to 1 degree, and that it became established after 10.6 m.y. ago. could well have resulted from tilting caused by Still to be clarified are: (1) The environment the extensive faulting and epeirogenic warping of deposition of the Imperial and Bouse For- experienced by the area since the time when mations. (2) The temporal and stratigraphic the gravel beds were laid down. relations between the Imperial, Bouse, and The Peach Springs Tuff gives the youngest Muddy Creek Formations. (3) The presence of date currently available at which the north- Late Cretaceous coccoliths in both the Imperial easterly drainage from the area of the present and Bouse Formations. (4) The presence of Basin and Range province onto what is now Late Cretaceous foraminifers in the Imperial the Colorado Plateau was still active, and but not in the Bouse so far as is now known. therefore an upper age limit for major move- The Imperial Formation has been described ment along the Grand Wash fault. As the as a deltaic deposit of the Colorado River Muddy Creek Formation was deposited in the (Muffler and Doe, 1968). I would interpret the interior basins formed when faulting destroyed Bouse Formation in the same way, although this old drainage, the Peach Springs Tuff also both Metzger and Smith (1970, written gives a limiting value for the age of the Muddy commun.) disagree. It is not crucial to the Creek Formation in the area adjacent to the analysis presented here that either of these Hualapai Plateau. deposits be strictly deltaic, only that they be of The geology of the Hualapai Plateau shows Colorado River origin. But in my opinion, a that, until 18 m.y. ago or less, drainage was to deltaic environment of deposition is the one the northeast, down the structural and that best fits the known facts and most easily topographic slope, onto the plateau, and nearly leads to a reasonable interpretation of the early at right angles to the present trend of the history of the river. Colorado River; at an unknown, but probably The early river and its tributaries flowed in not great time after 18 m.y. ago, drainage large part over young and poorly consolidated became local and interior. basin deposits. Thus a large volume of detritus probably was carried by the Colorado River INTERPRETATION from its earliest times, even when the length of The information presented in this report for the river was considerably less than it is now. the four areas discussed is summarized in Table This detritus was brought into the Bouse em- 1. The information suggests that the various bayment; part must have settled out near the deposits considered to contain material of mouth of the river, part was probably carried fluvial origin do reflect an ancestral Colorado much farther into the Bouse embayment and River rather than other rivers, possibly un- presumably into the Imperial Sea as well. This related to each other. far-traveled fraction represents what might be In the Imperial Valley and Parker-Blythe- called large-scale "bottomset" beds, although Cibola area, there is no evidence for ancient the boundary between bottomset beds and major drainages other than that of the Colo- pelagic sediments that are mostly, but not en- rado, and considerable evidence pointing to an tirely of Colorado River derivation probably is ancestral Colorado River. In the Lake Mead a matter of individual definition. These "bot- area, a long period of widespread interior basin tomset" beds may well have constituted a conditions predated establishment of the Colo- substantial fraction of the fill of the Bouse rado River, which is the only through-flowing embayment and of the Salton Trough as well, drainage of such proportions for which there is particularly if sedimentation was accompanied record. And for both the Lake Mead area and by sinking of the area, as suggested for the Downloaded from gsabulletin.gsapubs.org on January 23, 2013

TABLE 1. STRATIGRAPHIC UNITS OF IMPORTANCE TO COLORADO RIVER HISTORY IN BASIN AND RANGE PROVINCE

Area Deposit Age Characteristics Environment of deposition Comments Imperi al Imperial Forma- Coarse grained sediments at Subaerial for coarse grained Imperial Formation Formation tion, late Mio- margins grading basinward marginal deposits. Marine marks first influx of and cene, or early into fine grained sand, silt, for fine grained deposits of far-traveled sediments younger Pliocene; may and clay. Sediments in cen- Imperial Formation, becoming of Colorado River type. rocks be as young as tral part of basin similar lacustrine and then sub- Younger fine grained early Pleisto- in grain size and mineralogy aerial in younger forma- deposits are mostly cene. to Colorado River material. tions. Imperial Formation laid down by the river. Contain Mancos-type Late deposited in northward ex-

T ' 1 Cretaceous foraminifers, tension of Gulf of Califor- I/alley and Cretaceous coccoliths. nia. Late Mostly Conglomerate and breccia Subaerial Materials derived from Cenozoic Miocene of granitic, dioritic, and erosion of local high- rocks of metamorphic composition, lands. p re- grading laterally (basin- Imperial ward) into finer-grained age rocks of the same composi- tion.

Bouse Pliocene. At Basal limestone, overlain Embayment of Gulf of Cali- Freshening of water and Formation least as old by interbedded sand, silt, fornia. Water shallow, the volume of sediments as 3.02 ± 1.15 clay; marginal tufa. In- brackish. Apparently was can only be explained m.y., probably terbedded unit has regular, fresher northward toward by proximity of large older. well -developed bedding; Topock and Needles river. Geographic lo- sand layers locally cross cation of Bouse sug- } bedded. arker- 31ythe- the Colorado. Cibola Fangl cm- Miocene(?) Cemented gravel and sand Debris aprons and wash de- Predates Bouse marine era te of local derivation. posits from surrounding transgression. highlands, at least in part subaerial .

Cemented Include basalt Very well rounded gravel in- Scattered remnants restric- Indicate Colorado had Colorado flow dated at terbedded with coarse cross- ted to valley of Colorado present course, and River 3.3 ± 0.4 m.y. bedded sand. Moderate cal- River, locally only a few had cut down to within gravels Late Pliocene cite cementation. Clasts hundred feet above present a few hundred feet of to early include wide variety of grade. Deposited when val- present grade, by Pleistocene. rocks present along Colorado ley had been incised and es- 3.3 ± 0.4 m.y. ago. drainage, but more resistant sentially had present con- lithologies predominate. figuration. Muddy Miocene(?) and Conglomerate, breccia, sand- Interior-basin deposits fill- No through-flowing Creek Pliocene. Young- stone, siltstone, chemical ing basins formed by basin- drainage. No major Formation er than Horse precipitates, vitric and and-range faulting. Deposits canyon at present Spring Formation vitric-crystal tuffs. Rapid reflect fans, pediments, mouth of Grand Canyon. (20 ± m.y,), lateral and vertical varia- bahadas* playas, saline Other canyons, as deep mostly older tion. Extensive inter- lakes. Some basins intercon- as the modern ones, than 10.6 m.y. tonguing of facies. Lava nected, others not. Tecton- but shorter, present In Hualapai Val- flows present locally. ism continuing during Muddy elsewhere along Grand ley, younger Creek time, but Muddy Creek Wash Cliffs; mostly than Peach Formation is much less de- choked by Muddy Creek .ake Mead Spring Tuff formed than older rocks. Ef- conglomerates and (18.3 ± 0.6 fusive and pyroclastic vol- breccias of local de- m.y. ) of Young canism active. rivation. (1966b), Horse Early and middle Fresh water limestone, dolo- One or more basins intermit- Predates most basin- Spring Miocene. Radio- mite, magnesite, tuff, ben- tently occupied by lakes and-range faulting in Formation metric ages on tonitic clay, intermixed rich in salts, fed by area. Deposited tuff cluster with detrital material streams flowing predominant- chiefly north of pres- around 20 m.y. ranging from shale to con- ly north. Region had con- ent Lake Mead. Ma- glomerate. siderable relief, was pos- terials mostly derived sibly tectonically unstable. from south. Pyroclastic volcanism out- side of area of deposition, probably to west. Willow Peach Springs Fanglomerate, conglomerate, Deposited in channels and on Deposits on the Huala- Springs Tuff, part of with interbedded siltstone, erosion surface cut into Pa- pai Plateau indicate Formation Hualapai Volcan- claystone, limestone, and leozoic rocks dipping gently drainage to the north- Hualapai ics and high in vol can i cs . Congl omerates northeast. Channels and sur- east and local ponding. Volcanics, section, dated are alternately of local face also dip gently north- None are related to the Buck and at 18.3 ± 0.6 (limestone) and of distant east. Far-traveled conglom- Colorado River. By Doe Con- m.y. Youngest (arkose) derivation. erates derived from Basin and Peach Springs Tuff glomerate, deposits (Willow Range province, which was (middle Miocene) time, higher than plateau. Locally the Grand Wash fault fuaiapai Westwater Springs Forma- Formation, tion) are Plio- derived conglomerates, as had already been ac- 'lateau Hindu Fan- cene(?) well as limestone and clay- tive, but movement was glomerate, stone, indicate interruption not sufficient to in- Music of drainage and local pond- terrupt drainage from Mountain ing, presumably resulting the Basin and Range Conglomer- from movements on Grand Wash area to the southwest. ate, all fault. Youngest deposit After Peach Springs of Young (Pliocene(?)) is locally de- Tuff time, major move- (19663, rived and may be correlative ments interrupted 1970). with the Muddy Creek Forma- drainage and formed tion. the Grand Wash Cliffs. Downloaded from gsabulletin.gsapubs.org on January 23, 2013 1944 I. LUCCHITTA

Salton Trough by Muffler and Doe (1968). Arizona and contributing material to the Bouse Eventually, shallowing of the water in the and perhaps to the Imperial from near Yuma Bouse embayment would have allowed the to the south. mouth of the Colorado River to migrate south- As there was no through-flowing drainage in ward, depositing foreset beds over the older the Lake Mead area until less than 10.6 m.y. "bottomset" beds and completing the filling ago, the bulk of sediments in the Bouse and of the embayment with sediments. The process the Imperial Formations is likely to be not would have continued into the Salton Trough, much older than that date. Conversely, it is and, indeed, to the modern delta of the river. likely that the beginning of deposition of the After deposition, the foreset beds would have Bouse and the Imperial sediments goes back to been subject to subaerial erosion by the river. considerably more than about 3.3 m.y. ago, for This, together with the large scale and the by that time the Colorado was a well established gentle dip, can explain why deltaic (that is, and incised stream in the Lake Mead region. foreset) structures are not visible in the out- Damon's (1972, oral commun.) date on the crop. But the interbedding of sand, silt, and Bouse Formation shows that this formation clay, the abundance of sand in the section, the was already being deposited by 5.4 m.y. ago. channels filled with crossbedded sand described These dates are believed to bracket as Pliocene by Metzger (1968) all suggest that a delta, in the age of the Bouse and that part of the the sense used above, is indeed a reasonable Imperial Formation that contains Colorado environment for deposition of the Bouse For- River material. mation. For the Imperial Formation, the The distribution of the Mancos-type Late enormous volume of sediment of Colorado Cretaceous foraminifers and of the Late River origin and analogy with the modern Cretaceous coccoliths is puzzling. If both types delta suggest a similar origin. of microfossils were transported by the Colo- A specific objection to the delta hypothesis rado River, how could the Imperial Formation for the Bouse Formation has been raised by contain both, and the Bouse, farther upstream Metzger (1970, written commun.), who points along the course of the same river, the coc- out that in a well near Parker, Arizona, fora- coliths but not the foraminifers? Two explana- minifers are present throughout the 767 ft of tions can be advanced: (a) When the coc- section. This would indicate uniform salinity colith-bearing part of the Bouse Formation for the time interval represented by these was being laid down, the Colorado River (or rocks, serving evidence against the gradual the Gila drainage) had begun eroding rocks encroachment of the river in the area. How- containing the coccoliths, but not the Mancos ever, little is known about how much section and its foraminifers. By the time the delta of has been eroded from above the 767 ft now the river had reached the Imperial Valley area, present, which could well represent mostly both coccolith-bearing and Mancos rocks were "bottomset" beds laid down at some con- being eroded, (b) The coccoliths were derived siderable distance from the mouth of the river. from local sources. Moreover, the presence of foraminifers does Although the first possibility cannot be not necessarily indicate that they lived where excluded, the second seems simpler and more they were buried; in an environment like that plausible, especially as the coccoliths are a postulated for the Bouse, most, or even all, of widespread species, by no means restricted to the foraminifers could be brought by tides and the Cretaceous of the Colorado Plateau. David currents into localities where they would not Bukry (letter to Metzger, 1968) points out normally live. that for three areas inspected, though ad- The disagreement on whether the Imperial mittedly a small sample, the abundance of and Bouse Formations are deltaic probably coccoliths increases from the Bouse of the Big stems chiefly from how one defines a delta. In Maria Mountains (about 15 mi north of Ely the) any case, it is likely that the deposits in ques- to the Imperial of the Coyote Mountains tion are mostly of Colorado River origin, with (western side of Imperial Valley). This would subordinate contributions from drainages head- suggest dispersal of coccoliths by marine cur- ing in the Basin and Range province. A possible rents of the Gulf in Imperial and Bouse time exception, in terms of volume of sediment from a source area in the Peninsular Range as contributed and of source area, could be an far as the Bouse embayment, which is not un- early Gila River drainage, heading in central reasonable in terms of the distances involved. Downloaded from gsabulletin.gsapubs.org on January 23, 2013 EARLY HISTORY OF COLORADO RIVER 1945

The Late Cretaceous foraminifers are a sitional between the Imperial and the Bouse, greater problem because their provenance is would mark the time when the Colorado cut not local. Their presence in the Imperial through the upwarp. Formation and absence in the Bouse can be The second model seems to run into the explained most readily in two ways: fewest difficulties, and is therefore used in the 1. The foraminifers were carried by the following synthesis. early Gila-Salt River drainage and deposited from near Yuma, where the drainage presum- SYNTHESIS ably emptied into waters of the Gulf of Cali- The information and the speculations pre- fornia, generally westward toward and into the sented in this report can be synthesized as Salton Trough area. The headwaters of this follows, attempting to tie together the data river system could have reached Upper Cre- now available into a consistent, though pain- taceous foraminifer-bearing rocks in Central fully tentative, account of the early history of Arizona. While this was taking place, the the Colorado River in the Basin and Range Colorado River would not yet have reached province. areas of outcrop of the Mancos Shale, and the 1. Until some unspecified time after 18 m.y. sediments contributed by the Colorado to the ago (Peach Springs Tuff time) major basin- Bouse Formation in the Parker-Blythe-Cibola range faulting had not yet occurred in the area therefore would not contain the foramini- Lake Mead area. The Colorado Plateau was fers. This hypothesis implies (a) an abundance topographically low, the Basin and Range of the Late Cretaceous foraminifers in the province to the west relatively high. Drainage Bouse of the Yuma area; (b) a gradual decrease was northeast onto the plateau and north. The in the abundance of these foraminifers in the Colorado River did not exist. Vulcanism Bouse as one goes northward from Yuma produced lava and welded tuff that flowed toward the Parker-Blythe-Cibola area, as un- onto the Hualapai Plateau. doubtedly some of the foraminifers would have 2. Between about 18 and 10 m.y. ago, basin- been dispersed in that direction; (c) a low- range faulting occurred in the Lake Mead area salinity anomaly in the vicinity of Yuma; and and possibly farther west, resulting in the (d) a mineralogic and perhaps textural dif- structural and topographic differentiation be- ference between the Bouse at Yuma and the tween the plateau and the Basin and Range same formation farther north. None of these province. Tectonic basins were formed and characteristics has been detected so far, al- filled by interior-basin deposits (Muddy Creek though admittedly work in the Yuma area has Formation) in the Lake Mead area. Pre-existing not been sufficient to determine this beyond drainage was disrupted, and interior drainage doubt. became widespread. The Colorado River still 2. When the sediments now present in the did not exist. Subaerial fanglomerate material Parker-Blythe-Cibola area as the Bouse was deposited in the Parker-Blythe-Cibola Formation were being laid down, the Colorado area. On the Hualapai Plateau, drainage be- River had not yet extended headward to came interior and was accompanied by the areas on the Colorado Plateau where the deposition of locally derived material. Mancos Shale cropped out. By the time the 3. Between about 10 and 3.3 m.y. ago, but headwaters of the river had reached areas un- probably no less than 5.4 m.y. ago, waters of derlain by the Mancos Shale, the Bouse embay- the Gulf of California encroached into the ment was mostly or entirely filled up, and the Parker-Blythe-Cibola area, forming the Bouse locus of heaviest deposition had shifted to embayment. Drainage in the Parker-Blythe- somewhere between the Parker-Blythe-Cibola Cibola, Lake Mead, and Hualapai Plateau areas area and the Salton Trough. Probably, the area became integrated and through-flowing, prob- of outcrop of the Mancos at the time was gen- ably by headward erosion, and formed the erally east of the Kaibab upwarp, as suggested ancestral Colorado River. The river emptied by original non-deposition westward, rapid into the Bouse embayment, progressively westward facies change from shale into sand- filling it and advancing toward the Salton stone and conglomerate, and extensive early Trough area. The fine-grained fraction from and middle Cenozoic erosion. Therefore, the the river sediments may have been widely first appearance of Mancos foraminifers in the distributed in the upper Gulf of California, Imperial Formation, or in sediments tran- some of the material possibly being deposited Downloaded from gsabulletin.gsapubs.org on January 23, 2013 1946 I. LUCCHITTA

in the Salton Trough area as offshore deposits. Imperial time is a difficult undertaking, as the Conversely, fine-grained material and detrital Parker-Blythe-Cibola area and the Imperial Cretaceous coccoliths of local derivation prob- Valley are separated by the San Andreas fault ably were carried into the Bouse embayment zone. On the other hand, an improved under- by marine currents. At this time, the head- standing of the lithosomes in the Bouse and waters of the river had not yet reached areas Imperial Formations may shed some light on where the Mancos Shale cropped out. the amount, rate, and timing of deformation When the delta had advanced to some point along the San Andreas fault in the region. between Parker-Blythe-Cibola and the Salton Trough, the headwaters of the river reached ACKNOWLEDGMENTS areas where the Mancos Shale was exposed, My understanding of the geology and the probably east of the Kaibab upwarp. In cutting problems involved in this study has been across the upwarp, the river may have captured greatly enhanced by discussions and correspon- an ancestral upper Colorado River postulated dence with the late E. C. Allison, and O. L. by McKee and others (1967). Bandy, David Bukry, P. E. Damon, D. G. As the delta of the Colorado River advanced Metzger, L. J. Muffler, P. B. Smith, and R. A. toward the Salton Trough, which it eventually Young. In addition, I have received valuable filled with a great thickness of deltaic deposits, advice from Baerbel Koesters-Lucchitta. D. G. the older deltaic sediments in the Parker- Metzger, J. P. Schafer, and P. B. Smith Blythe-Cibola area were eroded and capped have kindly reviewed the manuscript and made unconformably by a veneer of Colorado many useful suggestions. Responsibility for the River alluvium, although locally the alluvium views presented here is strictly mine. In fact, may have been deposited directly on the delta Metzger and Smith disagree with some of my sediments without an intervening period of conclusions, as outlined in this paper. erosion. My work in the upper Lake Mead area was As the delta filled the Salton Trough, con- supported by grants from the Museum of ditions gradually changed from marine to Northern Arizona and from the Penrose deltaic to subaerial. The delta then continued Bequest of the Geological Society of America. to build up into the Gulf of California, as it does today. REFERENCES CITED 4. By about 3.3 m.y. ago, the Colorado River Allison, E. C., 1964, Geology of areas bordering had cut down to almost its present depth in Gulf of California, in van Andel, Tj. H., and the upper Lake Mead area, only a few miles Shor, G. G., Jr., eds., Marine geology of the west of the plateau. Clasts in the river gravel Gulf of California—a symposium: Am. Assoc. of this age are well rounded, far traveled, and Petroleum Geologists Mem. 3, p. 3-29. represent a variety of the lithologic types ex- Anderson, R. E., Longwell, C. R., Armstrong, posed in the Grand Canyon. A well-developed R. L., and Marvin, R. F., 1972, Significance of Grand Canyon existed at that time. K-Ar ages of Tertiary rocks from the Lake As a consequence of the hypothesis presented Mead Region, Nevada-Arizona: Geol. Soc. here, the Imperial would in part be younger America Bull, v. 83, p. 273-288. Armstrong, R. L., 1963, Geochronology and than the Bouse, in part a time-equivalent off- geology of the eastern Great Basin in Nevada shore facies of the Bouse delta. But even for and Utah [Ph.D. thesis]: New Haven, Conn., the parts differing in age, the difference could Yale Univ. be small in terms of geologic time. The horizon Damon, P. E., 1965, Correlation and chronology of at which the Mancos foraminifers first appear ore deposits and volcanic rocks: Univ. Arizona, should be at the present topographic surface Geochronology Lab., Ann. prog. rept. COO- somewhere between the Bouse and the Imperial 689-50, 75 p. areas and should dive progressively deeper as 1968, Correlation and chronology of ore one approaches the Imperial Valley. This deposits and volcanic rocks: Univ. Arizona, Geochronology Lab., Ann. prog. rept. COO- horizon should provide a reasonably good time 689-100, 75 p. marker and would indicate the time when the 1970, Correlation and chronology of ore Colorado River cut across the Kaibab upwarp deposits and volcanic rocks: Univ. Arizona, and possibly captured a pre-existing upper Geochronology Lab., Ann. prog. rept. COO- Colorado River. An accurate reconstruction of 689-130, 77 p. the course followed by the river in Bouse and Dibblee, T. W., Jr., 1954, Geology of the Imperial Downloaded from gsabulletin.gsapubs.org on January 23, 2013 EARLY HISTORY OF COLORADO RIVER 1947

Valley region, California, Pt. 2, in Jahns, R. H., of upper Cenozoic sediments in Colorado delta ed., Geology of southern California, Chap. 2: region: Jour. Sed. Petrology, v. 35, p. 911-916. California Div. Mines Bull. 170, p. 21-28. Metzger, D. G., 1968, The Bouse Formation Durham, J. W., 1950, Megascopic paleontology and (Pliocene) of the Parker-Elythe-Cibola area, marine stratigraphy, Pt. 2; 1940 E. W. Scripps Arizona and California, in Geol. Survey re- Cruise to the Gulf of California: Geol. Soc. search 1968: U.S. Geol. Survey Prof. Paper America Mem. 43, 216 p. 600-D, p. D126-D136. Durham, J. W., and Allison, E. C., 1960, The Muffler, P.L.J., and Doe, B. R., 1968, Composition geologic history of Baja California and its and mean age of ditritus of the Colorado River marine faunas: Systematic Zoology, v. 9, p. delta in the Salton Trough, southeastern Cali- 47-91. fornia: Jour. Sed. Petrology, v. 38, p. 384-399. Hunt.C. B., 1969, Geologic history of the Colorado Smith, P. B., 1970, New evidence for Pliocene River, in The Colorado River region and John marine embayment along the lower Colorado Wesley Powell: U.S. Geol. Survey Prof. Paper River area, California and Arizona: Geol. Soc. 669, Sec. C, p. 59-130. America Bull., v. 81, p. 1411-1420. Longwell, C. R., 1936, Geology of the Boulder Tschanz, C. M., 1960, Regional significance of some Reservoir floor, Arizona-Nevada: Geol. Soc. lacustrine limestones in Lincoln County America Bull., v. 47, p. 1393-1476. Nevada, recently dated as Miocene, in Geol. 1946, How old is the Colorado River?: Am. Survey research 1960: U.S. Geol. Suivey Prof. Jour. Sci., v. 244, no. 12, p. 871-935. Paper 400-B, p. B293-B295. 1963, Reconnaissance geology between Lake Young, R. A., 1966a, Cenozoic geology along the Mead and Davis Dam, Arizona-Nevada: U.S. edge of the Colorado Plateau, in northwestern Geol. Survey Prof. Paper 374-E, 51 p. Arizona [Ph.D. thesis]: Washington Univ., Longwell, C. R., Pampeyan, E. H., Boyer, Ben, 115 p. and Roberts, R. J., 1965, Geology and 1966b, Cenozoic geology along the edge of the mineral deposits of Clark County, Nevada: Colorado Plateau in northwestern Arizona Nevada Bur. Mines Bull. 62, 218 p. [abs.]: Dissertation Abstracts, v. 27, no. 6, p. Lovejoy, E.M.P., 1969, Grand Wash problem at 1994-1995. Grand Canyon: Geol. Soc. America, Abs. with 1970, Geomorphological implications of pre- Programs for 1969, v. 1, pt. 5, p. 46. Colorado and Colorado tributary drainage in Lucchitta, Ivo, 1966, Cenozoic geology of the upper the western Grand Canyon region: Plateau, v. Lake Mead area adjacent to the Grand Wash 42, no. 3, p. 107-117. Cliffs, Arizona [Ph.D. thesis]: Pennsylvania State Univ. McKee, E. D., Wilson, R. F., Breed, W. J., and MANUSCRIPT RECEIVED BY THE SOCIETY AUGUST 9, Breed, C. S., eds., 1967, Evolution of the 1971 Colorado River in Arizona: Mus. Northern REVISED MANUSCRIPT RECEIVED JANUARY 27, 1972 Arizona Bull. 44, 68 p. PUBLICATION AUTHORIZED BY THE DIRECTOR, U.S. Merriam, Richard, and Bandy, O. L., 1965, Source GEOLOGICAL SURVEY