THIS
For the Climatic Change idiots:
http://geochange.er.usgs.gov/sw/impacts/hydrology/state_fd/cawater1.html
Note the 1860's. The Yuba River DRIED UP.
I remember the flood of December, 1964. It washed out part of a bridge near the NE corner of my Dad's and Uncle's property, and several acres at the NW corner. I don't remember the drought when the Yuba River dried up,

, but the Yuba is a tributary of the Sacramento River, which empties into San Francisco Bay. The Sacramento flows through the northern half of the Central Valley (the Sacramento Valley, for the terminally geographically curious). In all likelihood,
at least half of the Central Valley was severely affected, and the southern half, the San Joaquin Valley (and River) were probably affected just as severely.
Periodic droughts and flooding are normal for CA, and an H-5 for supplying the data that shows this better than my memory! Two things have made the current drought felt so severely. Federal courts have restricted the amount of water that can be drawn from the San Joaquin (and possibly the Sacramento) River(s) for use by farmers and Central Valley cities. Worse still, Since the early 70s, the Enviros have all but stymied the creation and expansion of new reservoirs, and have, IIRC, managed to get one or more emptied and returned to "nature". During that time CA population has more or less doubled, so the net effect is that CA is more easily and severely hurt by even brief droughts. So while the current drought is natural-cyclical, government has significantly exacerbated it.