California gets massive rains from atmospheric rivers periodically.
When Leland Stamford was sworn in as Governor in 1862, Sacramento was so flooded he had to take a boat to his inaugural.
William Brewer, hired by the State to survey the area, reported extensively on the event, which left the Central Valley under 30 feet of water. See his notes in 'Up and down California'.
Imho, the interesting element is his offhand comment that the native Indians had all moved to higher ground before the event, so they knew what was coming, unlike the incoming settlers.