Salton Basin lies along the complex boundary between the North American and Pacific plates. It represents part of an extensive transtensional rift system and is the northward landward extension of the Gulf of California. Salton Basin has been accumulating feldspathic sand shed from crystalline basement rocks in adjacent mountains, and lithofeldspathic sand derived from the Colorado River drainage basin or from older Neogene sands containing Colorado River detritus. From about 700 to 1580 A.D., ancient Lake Cahuilla had a significant effect on the geographical distribution and redistribution of Salton Basin sediments. Sand petrofacies recognized in Salton Basin are geographically controlled, and include: (1) Algodones Dunes and East Mesa area sands, (2) Lake Cahuilla sands (south), (3) Lake Cahuilla beach sands, (4) Basin-margin sands, and (5) Lake Cahuilla sands (north). The Algodones Dunes and East Mesa area sands were probably derived from reworked Neogene sediment. The reworked sands were transported via the Lake Cahuilla beach to the vicinity of Flowing Wells Siding and Mammoth Wash, where wind transported the sands to the Algodones Dunes and East Mesa area. Lake Cahuilla beach sands are variable in character. For example, sands in the vicinity of Hot Mineral Springs are volcanic-rock-fragment-rich and quartz-poor, whereas, sands in the area of Flowing Wells Siding and Mammoth Wash are quartz-rich and relatively volcanic-rock-fragment-poor. Sands from Lake Cahuilla (south) are compositionally similar to sands in the Borrego Formation which crops out in the San Felipe Hills and Bat Caves Buttes. Thus, petrologic data support the idea that sands on the eastern side of Lake Cahuilla were tranported south by longshore currents. Basin-margin sands and Lake Cahuilla sands (north) from the perimeter of Salton Basin, are composed of feldspathic material derived from crystalline basement in adjacent mountains. Medium-grained sand from Salton Basin was arbitrarily divided into four groups based upon the percentage of quartz in Q(F+A)R modes. The four groups of sand have variable compositions that are source-rock dependant, and superficially mimic changes produced by different climates. Thus, sandstone petrologists should be wary of inferring climatic conditions based solely on sand or sandstone compositions. Data presented here clearly indicate that source-rock composition is an important variable that has not been adequetely addressed in the climatic-discrimination models of Basu (1976) and Suttner and Dutta (1986).