GEOLOGY AND HYDROLOGY OF SELECTED PLAYAS IN WESTERN UNITED STATES

The playas studied during this investigation may be divided into fine-grained playas Rogers, Rosamond, Coyote Playas, California, and Big Smoky Playa, Nevada and coarse-grained playas Troy Playa, California, and Clayton Playa, Nevada. The fine-grained playas are characterized by 1 deposits of medium silt through fine clay size, 2 slow artesian and capillary movement of water through the surface, 3 mostly smooth, hard surfaces, and 4 current formation of giant desiccation polygons in many of the playas. The coarse-grained playas are characterized by 1 deposits of sand, silt, and in some cases evaporites, 2 rapid capillary discharge, 3 a water table that nearly coincides with the playa surface, and 4 soft, surficial sediments. The surface morphology of most playas is related to several factors including the rate of capillary discharge producing puffy ground, and the frequency of surface-water flooding producing smooth, hard ground. Also, capillary discharge combined with deposition of mud from floods has transformed roots and water- transported plants into highly irregular knobby ground in some playas, including Clayton. Playas are dynamic landforms that change.