hi
As a geologist , I can answer this Q' only after a serious investigating in the place. There can be more than one reasons for such event.
As to now - I can just copy (for you) what was written in the local newspaper:
Geologists aren't sure what caused the earth to open up. Apparently, the soil was saturated, but the source of the water was not immediately clear.
Some nearby residents told the Los Angeles Times they had a similar problem about a year ago when water gushed from the same property, sending mud into their backyard.
At first, firefighters suspected that a break in a water main undermined the home at 15940 West Skytop Road, but Department of Water and Power workers later determined that was not the case.
No significant movement was reported overnight. Experts do not believe the structure will slide off its foundations, but the fissure could continue to widen for some time, a fire department spokeswoman said.
