QUATERNARY GEOLOGIC MAPPING IN THE DESERT HOT SPRINGS AREA, RIVERSIDE COUNTY, CALIFORNIA: DATA TO ADDRESS SOCIETAL NEEDS AND GEOSCIENCE ISSUES

New geologic mapping of Quaternary and late Tertiary deposits and structure in the Desert Hot Springs and Seven Palms Valley 7.5' quadrangles and adjoining area is part of the Southern California Areal Mapping Project (SCAMP). This mapping provides data needed to address issues of seismic, flood, debris-flow, and blowing-sand hazards; groundwater hydrology; aggregate resources; and ecosystem habitat, such as for endangered species. The map area includes parts of the Banning and Mission Creek Faults of the southern San Andreas Fault (SAF) system between and including the northwest part of the Indio Hills and the deformed, uplifted sediments east of the Whitewater River. We use soil properties, associated surface characteristics, and lithostratigraphy to distinguish mappable surficial units. Extensive alluvial fans of probable late Holocene age are dominated by bouldery debris-flow deposits that have very weak, non-oxidized soils. These deposits are apparently not faulted where they overlie buried parts of the SAF system. Older deposits are variably faulted, folded, and tilted. A fan remnant map unit of probable early Holocene to latest Pleistocene (?) age has oxidized soil that contains substantial eolian dust, but this unit lacks the distinctive red brown argillic (Bt) horizon present in more deformed Pleistocene sediments that flank valley margins and uplifts. Older gravelly deposits form eroded ridges. Basin-fill gravel, sand, and mud of the Palm Springs Formation of Dibblee (1954) and equivalent units comprise variably but locally highly deformed strata in the Indio Hills and at localities north and west of Desert Hot Springs. Young and active eolian sand is mapped separately as dunes and as sand ramps forming mantles on slopes of the Indio Hills.