The mineralogical composition of 50 samples of Recent sands and clays from Lucerne Dry Lake, San Bernardino County, California, was determined by X-ray diffraction. Areal variations in the distribution of the major mineral components were studied and compared with basin geometry and geology of the watershed areas in order to illustrate geological controls on fine sediment mineralogy within an isolated desert-lake basin. The major silicate and carbonate minerals are of detrital origin; relative abundance of these decreases toward the center of the basin, where halite and gypsum are concentrated. The San Bernardinos on the south, and Granite and Ord Mountains on the north, contributed quartz, feldspar, and hornblende. The carbonate distribution pattern suggests that the San Bernardinos also contributed detrital calcite and dolomite, probably derived from outcropping late Paleozoic marbles. The clay-mineral suite is dominantly illite and chlorite, with minor kaolinite and montmorillonite. Minor clay-mineral variations can be ascribed to source influences. The San Bernardinos contributed more chlorite and better crystalline illite (probably of metamorphic derivation) than the Ord and Granite mountains. There is no evidence of major diagenetic change of the detrital clay-mineral suite in the saline lake waters.

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