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A group of tourists observes a subsidence at Rico Hill ("Sumaj Urqu" in Quechua language, meaning beautiful or majestic hill) in Potosi, Bolivia, on September 21, 2010. Rico Hill is one of the biggest silver deposits of the world and a symbol in the Bolivian emblem. Five hundred years of exploitation have left over 600 pitheads and 90 kilometers of tunnels.
Just south of the San Joaquin Valley Delta lies some of California's most fertile farming lands in the world. But to keep the crops green, farmers use groundwater, they pump it from wells deep underground.
That creates a rather troubling effect called subsidence, or the sinking of the earth. Here with more is hydrologist Jay Famiglietti, director for the UC Center for Hydrologic Modeling at UC Irvine.