The Salton Sea, originally a fresh-water lake formed by the flood of the Colorado River in 1905, is located in the center of the Colorado Desert of California. By 1929, the water of the lake had become almost as saline as ocean water because of intense evaporation and solution of salts present on the floor of the basin before the flood. In recent years, in spite of the high rate of evaporation, excessive runoff from irrigation water has maintained and even raised the level of the lake.

Evaluation of the water budget has made it possible to anticipate future changes in the chemical composition of the water—i.e., an increase in the amount of sulfates is predicted for the future. Measurements with a current cross and studies of salinity distribution indicate a counter-clockwise current pattern in the Salton Sea.

Sands, silts, and clays are deposited in that order from the shore line to the center of the lake. The water content, amount of calcium carbonate, and textural characteristics indicate that most of the sediments of the Salton Sea were derived from the suspended load of the Colorado River, whereas the mineralogical study suggests that some of the sediments have a local origin. Two entirely different methods of computing the rate of sedimentation and of calculating the amount of calcium carbonate in the sediments give results of the same order of magnitude. The large amount of calcium carbonate is partly due to precipitation and partly to transportation by Colorado River water.

Foraminifera are the most abundant microorganisms in the lake. Several ecological factors influence their distribution; among these factors, chlorinity and temperature are not important, depth may be important by its effect on other factors, but the variation in the pH of the sediments is significant. The living foraminiferal assemblage is due to accidental introduction, but the natural effect of environmental conditions has resulted in the creation of a dwarf fauna and many malformed individuals. In contrast to conditions in the ocean, abundance of species decreases offshore; however, as in the ocean, the number of living Foraminifera increases greatly after a bloom of phytoplankton. The average productivity of the Salton Sea is greater than that of the oceans.

Conclusions derived from this study were applied to sediments deposited in the same basin during the past and made it possible to suggest a late Pliocene or early Pleistocene age for the Borrego formation and a Pleistocene age for the Brawley formation.

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