There are a number of modern prophecies circulating around the world from both major and minor sources of a super earthquake on the west coast that will destroy large parts of California, Oregon, Washington State, and other areas along the western coastline.  Some believe this may be caused by an unzipping of the Cascadia faultline which presently is the only known fault with sufficient enough potential energy to create such a quake.  There has also been extensive discussion that, should this earthquake occur, it will create a subsequent tsunami tens, even hundreds of feet tall that would sweep inland for a distance of between 60 and 100 miles.

Any city situated along the west coast, including Los Angeles and San Francisco, would be completely destroyed.  There is also discussion that this earthquake could cause the continental shelf in that area to sink upwards of 40 feet or more, and in some places up to as much as 200 feet, causing some areas to figuratively "fall into the sea" and never be seen or heard from again.  This will leave cities such as Los Angeles and San Francisco completely and permanently under water, never to again be inhabited.

Special Note: There are some theories that, should the wave reach far enough inland, it will fill the inner areas of California with so much water that it'll create a permanent inland lake (a large subsistence of the land would also create the necessary conditions for this to occur too) either in the central valley or even death valley.  Even if the lake isn't permanent, just the sea water inundation alone will make large swaths of California's aquifer undrinkable, and unusable, as well as the farmland that is touched by the sea water.  This means that anywhere the tsunami touches will cease to be inhabitable.  This is presnetly only theory, but it does help to explain the incredible amounts of damage that would be caused by such an event.