Claim: The ARkStorm occurs on average every 50 years with the largest event being 300% more powerful than any other floods recorded.
Evidence: The USGS sediment research in the San Francisco Bay Area, Santa Barbara basin, Sacramento Valley, and Klamath Mountain region have indicated that "megastorms" similar to the ARkStorm scenario have occurred in the following years A.D.: 212, 440, 603, 1029, c. 1300, 1418, 1605, 1750, 1810, and December 1861–January 1862 (the latest occurrence). 
The largest event was the one in 1605, which left behind a layer of silt two inches thick, indicating that this flood was at least 50% more powerful than any of the others recorded.