Our central valley was once a lake. Well more like marsh land. They figured out that the flat land of the central valley was fertile to grow agriculture so they did things to empty out that body of water. Building dams, building levees and what not. Of all of these times, I did not know until I did my research. Our delta water ways levees are man made to hold the water back otherwise, it will spill onto the flat land and become a marsh. So basically, From sacramento to bakersfield or driving along the 99, all that used to be underwater. Did they teach this in school? I surely slept through it because I serious do not remember or maybe they did not.