600,000 plus year ago, the central valley of California was flooded by a shallow lake, large enough to rival Lake Michigan in area. The end of the Ice Age caused the Sierra Nevada glaciers along the eastern border to melt, which eventually carved a new route to the sea. >This vast freshwater inland sea was not to last. Some 650,000 years ago, the Earth began to warm and the glaciers which held the Sierra Nevada in an icy grip began to melt. The water began to rush into the lake raising the water level. At the same time, tectonic uplifting of the Coast Range near Monterey left Lake Corcoran with no outlet to the sea. Something had to give and it did. Approximately 600,000 years ago, Lake Corcran carved a new outlet to the sea through what is now Carquinez Strait. The water poured through a low spot in the Coast Range carving a channel 100 feet deep between what are now Contra Costa and Solano counties and permanently draining Lake Corcoran and changing the landscape of the San Francisco Bay Area and the Central Valley forever.