Early last year, the hydropower company Nature and People First set its sights on Black Mesa, a mountainous region on the Navajo Nation in northern Arizona. The mesa’s steep drop offered ideal terrain for gravity-based energy storage, and the company was interested in building pumped-storage projects that leveraged the elevation difference. Environmental groups and tribal community organizations, however, largely opposed the plan. Pumped-storage operations involve moving water in and out of reservoirs, which could affect the habitats of endangered fish and require massive groundwater withdrawals from an already-depleted aquifer.

The Federal Energy Regulatory Commission, which has authority over non-federal hydropower projects on the Colorado River and its tributaries, ultimately denied th

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