"There's a passage in John Steinbeck's "East of Eden" that does a pretty good job describing California's rainfall patterns: The water came in a 30-year cycle. There would be five to six wet and wonderful years when there might be 19 to 25 inches of rain, and the land would shout with grass. Then would come six or seven pretty good years of 12 to 16 inches of rain. And then the dry years would come ..."