With its haunting rock spires and salt-crusted shores, Mono Lake is a Hollywood vision of the apocalypse. To the city of Los Angeles, however, this Eastern Sierra basin represents the very source of L.A.’s prosperity — the right to free water.

For decades, the Los Angeles Department of Water and Power has relied on long-standing water rights to divert from the streams that feed this ancient lake as part of the city’s far-flung water empire. But in the face of global warming, drought and lawsuits from environmentalists, the DWP is now facing the previously unthinkable prospect of ending its diversions there.