The Central Valley of California doesn’t begin so much with a gradual change in the landscape as with an abrupt line. Suddenly, a barren plain that looks like an apt cue for “The Good, the Bad and the Ugly” theme song is interrupted by the first row of leafy, irrigated crops.

Since the 1930s, the region has run on human control of water, carefully distributing the melting mountain snowpack through reservoirs and dams, pumping stations and irrigation pipelines, through drips, sprinklers and intentionally flooded fields.