West Mojave Plan FEIR/S - Desert Managers Group

Superior Dry Lake West consists of playa lakebeds near the southwest shore of SuperiorDry Lake. Fossil bone and tooth fragments have been reported and are thought to beRancholabrean (Woodburne 1978:53).Jack Rabbit Spring is at the north end of Coyote Dry Lake. Playa lake depositsreportedly contain fossil camel bones dating to possibly the Rancholabrean (Woodburne1978:54).Cronese is comprised of sediments from the Barstow Formation. The relatively sparsefossil mammals are important because they probably represent the youngest Barstovian-agesample in the Mojave Desert. They show a relatively evolved Merychippus and are associatedwith tuffs dated at 12.3 million years (Woodburne 1978:56).Alvord Mountain has a relatively thick sequence of tuffaceous sediment interbedded withtuffs and basalt flows, which is exposed in a valley drained by Spanish Canyon and its tributarieson the east flank of Alvord Mountain. The main fossil bearing unit is the Barstow Formation,followed by the Clews Fanglomerate and Spanish Canyon Formations of Hemingfordian age.Most of the fossils occur within a few feet in the middle of the Barstow unit. The stratigraphicsuccession of faunal remains corroborates the biostratigraphic and evolutionary sequence seen inthe Barstow Formation in the Mud Hills (Woodburne 1978:57).A series of sites occur in alluvial gravel, sandstone, and siltstone along bluffs overlookingthe Mojave River. The bluffs occur from the Daggett-Yermo are east to Camp Cady. Thesedeposits are Rancholabrean in age (Woodburne 1978:59).Manix-Afton Canyon. The Manix Lake Beds consist of a succession of fine-grainedlacustrine sediments interbedded with tufa and tuffs. They are unconformably overlain byalluvium and are cut by the Mojave River and its tributaries that flow into Afton Canyon.During the Pleistocene, Manix Lake extended westward into the Mojave Valley and north intopresent day Coyote Lake. This is one of the few well-studied Rancholabrean-age fossilassemblages, though much of the information is possibly unpublished as yet (60). The Manixbeds near Barstow, CA have yielded an assortment of fossil mammal remains, most of which arelimb bone fragments. This assemblage may be around 2 million years old, but evidence for exactdating is poor at present (Savage, Downs, and Poe 1954:53). Recovered specimens include truehorses (Equus), jackrabbits (Lepus), camelids, true deer (Odocoileus), pronghorns (Antilocapra),and tapirs (Tapirus) (Savage, Downs, and Poe 1954:56).The Cady Mountains comprise a relatively broad, sprawling range south of AftonCanyon. Like many Mojave ranges, a core of pre-Tertiary plutonic basement rock is overlain bya succession of mostly volcanic, then volcanic and sedimentary rocks that have been folded andfaulted and are roughly Miocene age. These are overlain by less extensive coarse-grainedapproximately Pliocene deposits and Quaternary fan deposits, which are all finally cut by presentstreams whose valleys are filled with alluvium. Fossils in the Cady Mountains are derived fromMiocene interbedded fluviatile clastic and tuffaceous sediments. The deposits are designated asthe Hector Formation, which is composed of coarse- to fine-grained alluvial deposits interbeddedwith tuffs and a basalt flow. Total thickness is approximately 1,500 feet.Chapter 3 3-290