Walk into any grocery store in America and there's a good chance the fresh produce you see there was grown in California. Up to half of the nation's fruit, nuts and vegetables are grown in the Central Valley, one of the planet's most fertile growing regions, between Los Angeles and Sacramento. Now, for the first time this century, the entire state is in severe to exceptional drought.
The San Joaquin River runs through the heart of this arid growing region and in a normal year would flow with fresh snow melt from the Sierra. But there's little snow in the mountains, and little water in the river.
To combat drought conditions, farmers and cities use water wells to tap underground aquifers. But those aquifers are overused and the rapidly declining water levels are causing the once water rich cavities to collapse in a process known as subsidence.