Been skimming the report a bit. The historical part is interesting. I had no idea that these megastorms have occurred in my home state every couple of centuries. When I first read the OP, I assumed the USGS must be talking about the East Coast or Midwest, not the West Coast. I mean, who thinks of the West Coast (California, in particular) when talking about catastrophic weather events?

Besides the loss of life, if the Central Valley of California ever flooded in a matter of days as they outline in the report, the agricultural loss and the loss of water, particularly to southern California, would be very painful. Most water districts could limp along for a while on stored water, but that will only last so long.

A massive earthquake could also cut us (southern California) off from our water supplies from Northern California, but I have a feeling that quake-damage may be quicker to repair than dealing with a massive flood. Repairs on quake damage could probably begin quickly, while just waiting for the floodwater to recede from an ARkstrom could take a very long time.

This ARkstorm report does make you look at the news from Queensland, Australia in a new light. That's another massive, massive flood event happening right before our eyes.