Late Quaternary geochronology and geomorphology of the Manix Basin, San Bernardino County, California

An investigation of the Manix basin in the central Mojave Desert indicates that at least three late Wisconsinan lakes filled the basin. Twelve new radiocarbon dates on critical lacustrine features, and fifteen new varnish age estimates on exposed surfaces throughout the Manix basin establish age limits on lake fluctuations and post-lacustrine erosion in the basin. Major lacustrine intervals occurred between approximately 31 and 29 ka, 21 and 17.5 ka, and 14.7 and 13.7 ka. The final lake in the Afton sub-basin was terminated by the rapid incision of Afton Canyon sometime between 13.8 and 13.3 ka. Lakes continued to exist in the Coyote sub-basin throughout the latest Pleistocene owing to Mojave River delta migration.; The maximum late Wisconsinan stage of Lake Manix was approximately 543 m above sea level, which is significantly lower than reported in previous studies. The maximum stage in Afton basin was probably stabilized by overflow into Coyote basin. Moreover, there is no evidence that Lake Manix spilled into the Silver/Soda Lake basin prior to the incision of Afton Canyon.; Three new fault and/or uplift zones have been identified and mapped on a 1:36,000 geomorphic map of the Manix basin. Offsets of strata with good age-control indicate that the region has been tectonically active during the late Quaternary. Furthermore, the tectonic origin of the Manix basin and its stratigraphic record appear to be closely tied to tectonic pulses and events in the distant San Bernardino Mountains.; Radiocarbon analyses of modern Anondonta califroniensis shells indicate that an approximate 450-year correction factor is necessary. Using this correction factor, more than 70 reported age estimates in the Mojave River basin have been revised and reinterpreted to present a comprehensive late Quaternary paleoclimatic history of the drainage basin.