DUST DEPOSITION IN SOUTHERN NEVADA AND CALIFORNIA, 1984-1989 - RELATIONS TO CLIMATE, SOURCE AREA, AND SOURCE LITHOLOGY

Dust samples collected annually for 5 years from 55 sites in southern Nevada and California provide the first regional source of information on modern rates of dust deposition, grain size, and mineralogical and chemical composition relative to climate and to type and lithology of dust source. The average silt and clay flux (rate of deposition) in s outhern Nevada and southeastern California ranges from 4.3 to 15.7 g/m (2)/yr, but in southwestern California the average silt and clay flux is as high as 30 g/m(2)/yr. The climatic factors that affect dust flux interact with each other and with the factors of source type (playas versus alluvium), source lithology, geographic area, and human disturb ance, Average dust flux increases with mean annual temperature but is not correlated to decreases in mean annual precipitation because the r egional winds bring dust to relatively wet areas. In contrast, annual dust flux mostly reflects changes in annual precipitation (relative dr ought) rather than temperature. Although playa and alluvial sources pr oduce about the same amount of dust per unit area, the total volume of dust from the more extensive alluvial sources is much larger. In addi tion, playa and alluvial sources respond differently to annual changes in precipitation. Most playas produce dust that is richer in soluble salts and carbonate than that from alluvial sources (except carbonate- rich alluvium). Gypsum dust may be produced by the interaction of carb onate dust and anthropogenic or marine sulfates. The dust flux in an a rid urbanizing area may be as much as twice that before disturbance bu t decreases when construction stops. The mineralogic and major-oxide c omposition of the dust samples indicates that sand and some silt is lo cally derived and deposited, whereas clay and some silt from different sources can be far-traveled. Dust deposited in the Transverse Ranges of California by the Santa Ana winds appears to be mainly derived from sources to the north and east.