California is sinking. In the Central Valley, the most productive agricultural region in the US, some areas drop an inch or two per year. Telephone poles slump, roads crack, canals fail. In time, all that sinking adds up. A recent state survey found one patch of farmland off I-5 near the town of Arbuckle had fallen 2 feet in nine years. The culprit: overdrafted aquifers. The process speeds up during periods of drought, when rivers run dry and farmers scramble to find other ways to water their fields.

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