Influence of late Quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont, eastern Mojave Desert

Radiocarbon dating of late Quaternary deposits and shorelines of Lake Mojave and cation-ratio numerical age dating of stone pavements (Darn. 1984) on the adjacent Soda Mountains Piedmont provide age constraints for alluvial and eolian deposits. These deposits are associated with climat-ically controlled stands of Lake Mojave during the past 15,000 yr. Six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and Piedmont surfaces, as well as on soil-geomorphic data. All but one of these stratigraphic units were deposited in response to time-transgressive climatic changes beginning approximately 10.000 yr ago. Increased eolian flux rates occurred in response to the lowering of Lake Mojave and a consequent increase in fine-sediment availability. Increased rates of deposition of eolian fines and associated salts influenced pedogenesis. stone-pavement development, and runoff-infiltration re-lations by (1) enhancing mechanical weathering of fan surfaces and hillslopes and (2) forming clay-and silt-rich surface horizons which decrease infiltration. Changes in alluvial-fan source areas from hillslopes to piedmonts during the Holocene reflect runoff reduction on hillslopes caused by collu-vial mantle development and runoff enhancement on piedmonts caused by the development of less-permeable soils. Inferred increases in early to middle Holocene monsoonal activity resulted i