Where Did the Sand Dunes Come From?

Tremendous earth upheavals that elevated the area above the ocean some 200 million years ago and the constant action of erosional forces over the eons have all had a part in sculpting this vast region.

For millions of years, the climate of California's desert region was tropical. As the earth's crust shifted along the San Andreas fault, the coastal mountains were pushed up, cutting off the moisture laden air coming from the ocean. At the same time, the interior plains of Southern California began to drop, forming a basin known as the Salton Sink. Gradually, the region dried, forcing many plants and animals to adapt or perish.

Ancient Lake CahuillaThe Colorado River flowed through country so flat that the course of the river varied over a wide area, being periodically diverted in one direction or another by silt deposits remaining after floods. Sometimes the river flowed into the Gulf of California, as it does today; other times it turned westward toward the Salton Sink. Each time the Salton Sink received the river flow, a large freshwater lake formed. Scientists refer to this ancient body of water as Lake Cahuilla. The last Lake Cahuilla covered much of the Imperial, Coachella and Mexicali Valleys as late as 1450.

The most popular theory holds that the Imperial Sand Dunes were formed from windblown beach sands of Lake Cahuilla. The prevailing westerly and northwesterly winds carried the sand eastward from the old lake shore to their present location. This process continues today. Prevailing winds cause the dunes to migrate southeast at the rate of approximately one foot per year.

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