The first fossils, marine shells from the ancient Sea of Cortez and fresh water shells from prehistoric Lake Cahuilla , precursor of the Salton Sea , were collected and described by William Blake in 1853. Blake was the geologist and mineralogist for the U.S. Pacific Railroad Exploration commissioned by Congress and President Pierce to find a railway route to the Pacific. It was Blake who first named this region the Colorado Desert.
Marine environments such as outer and inner shelf, platform reef, and near shore beach and lagoon are all represented within the Imperial Formation. As the sea shallowed, estuarine and brackish marine conditions prevailed, typified by thick channel deposits of oyster and pecten shell coquina that now form the Elephant Knees along Fish Creek.