Actually it is a tidal slough. If you go to 38°12'7.70"N, 122° 2'48.45"W you can see one that has water in it (in California). The snake used to be part of the Colorado River Delta, but since no fresh water makes it to the delta anymore, the delta has died out. The white is salt that has accumulated.

We killed the snake man! Save the wetlands and support wetlands restoration!