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Late Pleistocene fluviatile and lacustrine deposits in the Manix Lake basin occupy about 250 sq. mi. of the Mojave Desert including Coyote Lake and Toy Lake. The sediments have been exposed by recent downcutting of the Mojave River along part of the margin of the basin.
The lowest sediments are conglomerates that lie unconformably on metamorphic and volcanic basement rocks of the Cady Mountains. These alluvial-fan deposits dip gently to the northwest and interdigitate with lacustrine clays and silts in the center of the basin. About 70 ft. of fossiliferous lacustrine clays, silts, and sands lie horizontally above the conglomerates and older lake sediments. The uppermost sediments are alluvial arkosic sands and conglomerates that overlie the youngest lake beds, and are about 15 ft. thick.
Originally Manix Lake was restricted to the central portion of its basin and flanked by alluvial fans. As the basin was filled, lake sediments lapped on and covered over portions of the alluvial slopes. A wedge of fluviatile arkosic sand in the eastern part of the basin within the later lake beds may indicate a temporary retreat of the lake. A continuous sequence of lake beds near the center of the basin shows that one permanent lake was present until an outlet through Afton Canyon developed.
Fossil remains of fresh water gastropods, pelecypods, fish, tortoise, and water birds represent members of lake and lake-shore communities. Grassland and riparian communities are indicated by the following mammal genera: Canis, Felis, Equus, Camelops, Tanupolama, Ovis, Bison, Mammuthus, and Nothrotherium (not previously reported). A preliminary examination of the fauna reveals a Rancholabrean North American mammal age.
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