The San Joaquin Valley is a sediment-filled depression, called a basin, that is bound to the west by the California Coast Ranges, and to the east by the Sierra Nevadas. It is classified as a forearc basin, which basically means that it is a basin that formed in front of a mountain range.
The Valley began to form about 66 million years ago during the early Paleocene era. Broad fluctuations in the sea level caused various areas of the valley to be flooded with ocean water for the next 60 million years. About 5 million years ago, the marine outlets began to close due to uplift of the coastal ranges and the deposition of sediment in the valley. Starting 2 million years ago, a series of glacial episodes periodically caused much of the valley to become a fresh water lake. Lake Corcoran was the last widespread lake to fill the valley about 700,000 years ago. At the beginning of the Holocene there were three major lakes remaining in the southern part of the Valley, Tulare Lake, Buena Vista Lake and Kern Lake. In the late 19th and in the 20th century, agricultural diversion of the Kern River eventually dried out these lakes. Today, only a fragment of Buena Vista Lake remains as two small lakes Lake Webb and Lake Evans in a portion of the former Buena Vista Lakebed
The only constant in nature is change.
