San Diego Natural History Museum--Your Nature Connection[BRCC San Diego Natural History Museum: Paleontology]
Silent Beaches
Ancient Lake Cahuilla and its geologic setting

Salton Sea by Michael Fields
Resistant sandstone "sea" cliff on the west-facing ancient shoreline of Bat Cave Buttes, once an island in ancient Lake Cahuilla.
The modern Salton Sea lies near the middle of the Salton Trough, a northwesterly trending tectonic basin located between the Peninsular Ranges on the west and the Chocolate Mountains on the east. The area is characterized by numerous northwest-trending strike-slip faults, including from the San Andreas, San Jacinto, and Elsinore faults. Roughly 2000 square miles of the Salton Trough lies below sea level, and in many respects the area can be considered a landward extension of the Gulf of California. In fact, if it weren't for the Colorado River delta acting like a sediment "dam," the marine waters of the Gulf would extend all the way to Riverside County.

Abandoned fish camp at Salton Sea, photo by Michael Fields
Native Californians' abandoned fish camp constructed of sandstone concretions on the southwest shoreline of Lake Cahuilla.
Lake Cahuilla ( also called Lake LeConte) was a former freshwater lake that periodically occupied a major portion of the Salton Trough during the Holocene, approximately 10,000 to 240 years ago. There is debate among scientists over the exact timing and duration of inundation, with some workers proposing that the main period of lake formation was very recent -perhaps only 240 years ago. In contrast, other workers suggest that the main period of inundation was much older, perhaps as long as 10,000 years ago. Regardless of the exact timing of inundation, the former shoreline marking the maximum high stand for Lake Cahuilla is well-preserved around the margins of the Imperial Valley at an elevation of approximately 40 to 48 feet above sea level. At this maximum lake level Lake Cahuilla would have been over 300 feet deep, 105 miles long, and, at its widest point, some 35 miles across.

Salton Sea by Michael Fields
Ancient cobble beach and shoreline features of Lake Cahuilla.
Filling of Lake Cahuilla occurred several times during the Holocene, and each time the filling was the result of natural diversion of the Colorado River from its delta in the Gulf of California to the, below-sea-level Salton Trough. It is estimated that at present discharge levels it would take three years for the full flow of the Colorado River to fill the area of Lake Cahuilla. Once filled, the lake would overflow its natural levee to the south, allowing the Colorado to reestablish its flow into the Gulf of California. Eventually the river would bypass the lake completely by building a new levee. With the lake cutoff from recharge, it would gradually dry up. This cycle of flooding and desiccation is proposed to have occurred several times during the Holocene. Accidental filling of the area between 1905 and 1907 by a break in the manmade levee of the Colorado River resulted in formation of the present Salton Sea.

Text by Thomas A. Deméré, Ph.D., Curator of Paleontology; photos by Michael Fields, Senior Exhibit Designer