Welcome to, (yawwwwwwwn) California reality, S_P. I'm going to guess that the simian and the Mannn were both correct as to an earth slide and an earthquake - probably the latter triggered one of the former. Technically, I think this was along/near the San Gabriel Fault, but that's part of the San Andreas Fault system. And the LA and Ventura County areas are notorious for earth slides.
For some reason it seems pix like those don't inspire Progs to realize just how puny mankind is and how little we can actually affect this planet.