Research Paper THEMED ISSUE: CRevolution 2: Origin and Evolution of the Colorado River System II GEOSPHERE Reevaluation of the Crooked Ridge River—Early Pleistocene (ca. 2 Ma) age and origin of the White Mesa alluvium, northeastern GEOSPHERE; v. 12, no. 3 Arizona doi:10.1130/GES01124.1 Richard Hereford1, L. Sue Beard1, William R. Dickinson2, Karl E. Karlstrom3, Matthew T. Heizler4, Laura J. Crossey3, Lee Amoroso1, P. Kyle House1, 14 figures; 3 tables; 3 supplemental files and Mark Pecha5 1U.S. Geological Survey, 2255 N. Gemini Drive, Flagstaff, Arizona 86001, USA CORRESPONDENCE: rhereford@ usgs .gov 2Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721, USA 3Department of Earth and Planetary Sciences, University of New Mexico, 221 Yale Boulevard NE, Albuquerque, New Mexico 87106, USA 4New Mexico Geochronology Research Laboratory, New Mexico Bureau of Geology & Mineral Resources–New Mexico Institute of Mining & Technology, 801 Leroy Place, Socorro, New Mexico CITATION: Hereford, R. Beard, L.S., Dickinson, 87801, USA W.R., Karlstrom, K.E., Heizler, M.T., Crossey, L.J., 5Arizona Laserchron Center, Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721, USA Amoroso, L., House, P.K., and Pecha, M., 2016, Re- evaluation of the Crooked Ridge River—Early Pleis- tocene (ca. 2 Ma) age and origin of the White Mesa alluvium, northeastern Arizona: Geosphere, v. 12, no. 3, p. 768–789, doi:10.1130/GES01124.1. ABSTRACT older than inset gravels that are interbedded with 1.2–0.8 Ma Bishop–Glass Mountain tuff. The new ca. 2 Ma age for the White Mesa alluvium refutes the Received 27 August 2014 Essential features of the previously named and described Miocene Crooked hypothesis of a large regional Miocene(?) Crooked Ridge paleoriver that pre- Revision received 12 November 2015 Ridge River in northeastern Arizona (USA) are reexamined using new geologic dated carving of the Grand Canyon. Instead, White Mesa paleodrainage was Accepted 22 February 2016 and geochronologic data. Previously it was proposed that Cenozoic alluvium the northernmost extension of the ancestral Little Colorado River drainage Published online 7 April 2016 at Crooked Ridge and southern White Mesa was pre–early Miocene, the prod- basin. This finding is important for understanding Colorado River evolution uct of a large, vigorous late Paleogene river draining the 35–23 Ma San Juan because it provides a datum for quantifying rapid post–2 Ma regional denuda- Mountains volcanic field of southwestern Colorado. The paleoriver probably tion of the Grand Canyon region. breeched the Kaibab uplift and was considered important in the early evolu- tion of the Colorado River and Grand Canyon. In this paper, we reexamine the character and age of these Cenozoic deposits. The alluvial record originally INTRODUCTION used to propose the hypothetical paleoriver is best exposed on White Mesa, providing the informal name White Mesa alluvium. The alluvium is 20–50 m Cenozoic alluvium in a bedrock-bound paleovalley is perched on the Colo- thick and is in the bedrock-bound White Mesa paleovalley system, which rado Plateau in northeastern Arizona (USA) only 60 km east of the Grand Can- comprises 5 tributary paleochannels. Gravel composition, detrital zircon data, yon (Fig. 1; Hereford et al., 2013). The paleovalley’s possible significance to and paleochannel orientation indicate that sediment originated mainly from carving of the Grand Canyon is emphasized by a southwest-descending slope local Cretaceous bedrock north, northeast, and south of White Mesa. Sedi- toward the Grand Canyon and lag gravels derived from a distant source. This mentologic and fossil evidence imply alluviation in a low-energy suspended alignment points 300–400 km northeast, directly toward a possible source in sediment fluvial system with abundant fine-grained overbank deposits, indi- the San Juan Mountains of southwestern Colorado, and lag gravels in the cating a local channel system rather than a vigorous braided river with dis- study area apparently support such an origin. Minor amounts of pebble to tant headwaters. The alluvium contains exotic gravel clasts of Proterozoic small cobble gravel in the alluvium are composed of Proterozoic basement basement and rare Oligocene volcanic clasts as well as Oligocene–Miocene and Oligocene volcanic rocks (Lucchitta et al., 2011, 2013, fig. 10, Tables 1 and 2) detrital sanidine related to multiple caldera eruptions of the San Juan Moun- resembling those in the San Juan Mountains volcanic field (Lipman, 1989). The tains and elsewhere. These exotic clasts and sanidine likely came from ancient paleovalley is the topographically highest and therefore oldest geomorphic rivers draining the San Juan Mountains. However, in this paper we show that feature in this erosional landscape, suggesting substantial antiquity. These the White Mesa alluvium is early Pleistocene (ca. 2 Ma) rather than pre–early characteristics, i.e., proximity and slope toward the Grand Canyon, exotic grav- Miocene. Combined 40Ar/39Ar dating of an interbedded tuff and detrital sani- els, and assumed antiquity, led workers to conclude that the paleovalley was dine ages show that the basal White Mesa alluvium was deposited at 1.993 ± formed by an ancient river, probably the combined ancestral San Juan and For permission to copy, contact Copyright 0.002 Ma, consistent with a detrital sanidine maximum depositional age of Animas Rivers, that drained the late Paleogene San Juan Mountains volcanic Permissions, GSA, or [email protected]. 2.02 ± 0.02 Ma. Geomorphic relations show that the White Mesa alluvium is field (Cooley, 1960; Hunt, 1969; Stokes, 1973; Lucchitta et al., 2011, 2013). This © 2016 Geological Society of America GEOSPHERE | Volume 12 | Number 3 Hereford et al. | Reevaluation of the Crooked Ridge River Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/12/3/768/4092638/768.pdf 768 by guest on 26 September 2021 Research Paper Abajo S a Mtns n J u a n . Straight Cli M t n s Vallecito Res. upwarp s Monument Juan Ri n ve A Sa Blu r el l ver ow Ri e P Navajo Mtn Monument 37°N Lak UT CO B’ Paria Valley AZ NM Navajo Lees Ferry C h i Navaj Lake K Plt. K o Echo C Cree aibit r aibab e n l Animas e esa . k Carrizo e k o M r Skeleton e Cli Mtns iv R San NE Black Mesa (Table 1) s V o Plt. d a l l e y Figure 1. Study area in the eastern Grand a r h o s Canyon region of the southwest Colorado l B l a c a Chusk Juan o W Plateau, northeastern Arizona. Mtn— C Figure 2 o k t i mountain; Plt.—plateau; Res—reservoir. Cape b h e a Solitude Was n M e s a Basin pi in M o M k D G n Blue tns ra e o 36° n o e Canyon d n . C o n A’ a ny M Blue ash ko W p Pt. Cameron i P l ash t W Black Pt. olacca sh L P a B W it t o l Oraibi it e d d Bidahochi C Je ol Formation or ado ~16–2.5 0 50 100 km R ver iv Ma Ri e rco Flagsta r e Pu Chambers 112° Winslow 110° 108° W 35° conceptual paleoriver, called the Crooked Ridge River by Lucchitta et al. (2011, carving of the Grand Canyon (Lucchitta et al., 2011, 2013; Karlstrom et al., 2014, 2013), was thought to be involved in the early carving of the Grand Canyon; fig. 1 therein). The young age also disallows any relation between the alluvium overall the evolution of the canyon is a topic of debate (Karlstrom et al., 2012). and the Crooked Ridge paleoriver, which Lucchitta et al. (2013, p. 1427, 1430) This paper is a reassessment of the hypothetical foundations of the suggested was active during eruption of the 35–23 Ma San Juan Mountains Crooked Ridge paleoriver, i.e., its geomorphology, geology, depositional envi- volcanic field. Moreover, proposed correlation (Cooley et al., 1969; Hereford ronment, sediment source, and age. These key elements of the paleoriver are et al., 2013) of the alluvium with the mid-Miocene to late Pliocene Bidahochi examined using new (2013 and later) and unpublished data sets. The data in- Formation (Dallegge et al., 2003; Dickinson, 2013) seems impossible. Despite clude topical field mapping (Fig. 2), stratigraphy, sedimentology, pedogenesis, the exotic lag gravels, the presence of the ancestral San Juan River in the White carbonate geochemistry, detrital zircon provenance, sanidine geochronology, Mesa–Crooked Ridge area after 2 Ma is unlikely based on the substantial eleva- and tephro chronology. Among our principal findings is that the alluvium and tion difference between the low-elevation mid-Pleistocene (Wolkowinsky and associated paleovalley system are younger than ca. 2 Ma and older than 1.2– Granger, 2004) San Juan River and the relatively high elevation study area. 0.8 Ma, based on 40Ar/39Ar dating of tuff and detrital sanidine and inset rela- This and other information reported herein motivate us to recommend aban- tions between dated geomorphic surfaces. donment of the term “Crooked Ridge River” as applied to early Pleistocene This young age at the base of the alluvium in the White Mesa–Crooked deposits in the study area. The age, geology, and geomorphology of these Ridge area poses insurmountable problems for earlier interpretations. The age deposits are substantially different from those attributed to the Crooked Ridge precludes any connection between the paleovalley and all except the youngest paleoriver by Lucchitta et al. (2011, 2013). GEOSPHERE | Volume 12 | Number 3 Hereford et al. | Reevaluation of the Crooked Ridge River Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/12/3/768/4092638/768.pdf 769 by guest on 26 September 2021 Research Paper 111°30′ EXPLANATION 111°15′ Ka 111°0′W i White Mesa b it alluvium o Square Butte Dakota Sandstone Creek Je Entrada Sandstone a Je s WMZ-NUP Jn Navajo Je Sandstone Jn M e Measured R i d g e s B′ section Re PR-AZ-3* Plateau Detrital zircon d Highway Je quarry e and sanidine* M o r m o n Lake locality 36°30′N Figure 2.