Ark Storms of the Magnitude of the 1861-62 floods are projected to become more frequent and intense as a result of climate change.

The U.S. Geological Survey's (USGS) Multi Hazards Demonstration Project (MHDP) has prepared its second full scenario, called ARkStorm. The scenario addresses massive U.S. West Coast storms analogous to those that devastated California in 1861–62. Storms of this magnitude are projected to become more frequent and intense as a result of climate change.
The MHDP assembled experts from the National Oceanic and Atmospheric Administration (NOAA), USGS, Scripps Institute of Oceanography, the State of California, California Geological Survey, the University of Colorado, Federal Emergency Management Agency (FEMA), the National Center for Atmospheric Research (NCAR), California Department of Water Resources, California Emergency Management Agency (CalEMA) and other organizations to design the large, but scientifically plausible, hypothetical storm scenario that would provide emergency responders, resource managers, and the public a realistic assessment of what is historically possible.
The ARkStorm storm is patterned after the 1861–62 historical events but uses modern modeling methods and data from large storms in 1969 and 1986. The ARkStorm draws heat and moisture from the tropical Pacific, forming a series of Atmospheric Rivers (ARs) that approach the ferocity of hurricanes and then slam into the U.S. West Coast over several weeks. Atmospheric Rivers are relatively narrow regions in the atmosphere that are responsible for most of the horizontal transport of water vapor outside of the tropics.

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http://www.eoearth.org/view/article/51cbf0c17896bb431f6a2eeb/ 

I wasn't really aware of the fact that ARK storms would be more common in the future than in the past. So, because of this being aware when you are in a flood plain anywhere in California might be at some point a matter of life or death: Yours.

So, it becomes more important to be aware even when you are traveling through a California Flood plain anywhere to be more aware of the weather patterns than before.

I had written about the fact that if you look all around the world: "Why was there an area with so little City development here on the west coast when people first came here from Spain and the U.S. and Great Britain and Europe?

The answer might be that any city built on rivers (where people mostly build larger cities) would have been washed away every 150 to 200 years here in California for the last thousands of years. Only San Francisco which is built on hills would be immune to this because it has no flood plains only quick exits for rivers of water to the ocean. So, it is quite possible when the next Ark Storm hits the capital will once again have to move to San Francisco temporarily  again like it did in 1862 when Governor Leland Stanford moved by boat to San Francisco then with the state government because Sacramento was underwater for about 6 months.