We've talked about this before, but pumping from aquifers under the San Joaquin Valley is continuing to cause the valley floor to sink significantly:

Ground levels in some areas have dropped 1 to 2 feet in the last two years, creating deeper and wider “bowls” that continue to threaten the vital network of channels that transport water across Southern California, researchers say.

The findings underscore the fact that even as record rain and snow have brought much of California out of severe drought, some parts of the state will probably struggle with water problems for years to come.