plain sediments by the modern drainage have rendered relatively accessible for archaeological investigation a series of deposits that represent more than 350,000 years of Quaternary history. The Manix Basin, a structural basin in the central Mojave Desert, is the third and lowest major valley of the Mojave River, presently an exotic stream with episodic flow, which has its source in the San Bernardino Mountains, some to the southeast. A freshwater lake developed in the basin about 400,000 – 500,000 years ago near the Calico Archaeological Site. The lake was present until the late Pleistocene. The last high stand of Lake Manix was at and had a surface area of approximately . This lake drained, probably catastrophically, approximately 18,100 years ago, probably as a result of a major increase in river inflow or tectonic movement on the Manix fault. Fossils The lacustrine, fluvial, and alluvial sediments of the Pleistocene Manix Formation contain remains of numerous Rancholabrean animals ranging in age from approximately 20,000 years to well in excess of 350,000 years before present. Fossils recovered from the section include: camel, horse, mammoth, saber-tooth cat, dire wolf, short-faced bear, coyote, flamingo, pelican, eagle, swan, geese, mallard duck, ruddy duck, canvas backed duck, double-crested cormorant, grebe, crane, seagull and stork. Prehistoric tools Thousands of rocks that bear a strong resemblance to prehistoric tools have been found at the site, both on the surface, and up to below the surface. A stone from the Master Pit had been dated to over 200,000 BP. This date could have been the result of contamination from other elements in the soil, so currently there is an effort to date verified lithics through thermoluminescence dating. While the results are still pending, the styles suggest 20,000 to 30,000 BP. The debate centers on whether the "tools" were made by humans (i.e., artifacts), or through typical geological processes (i.e. geofacts). The general scientific consensus is that the subsurface items are geofacts. Artifacts or geofacts? The artifactual character of the Calico lithic assemblage has been questioned (Haynes 1973; Payen 1982a, 1982b; Taylor and Payen 1979; Duvall and Venner 1979). Haynes (1973) postulated that rock fracturing by tectonic stresses, weather, rock-on-rock percussion in streams and mudflows, pressure retouch of buried cobbles, and successive generations of flake removal and separation from cores through cycles of erosion and redeposition could have occurred during deposition of the alluvial deposits at Calico and produced specimens indistinguishable