Oakland, Calif.-based BrightSource Energy has been pushing for more than two years for permission to erect 400,000 mirrors on the site to gather the sun's energy. It could become the first project of its kind on U.S. Bureau of Land Management property, leaving a footprint for others to follow on vast stretches of public land across the West.

The construction would come with a cost: Government scientists have concluded that more than 6 square miles of habitat for the federally threatened desert tortoise would be permanently lost.

The Sierra Club and other environmentalists want the complex relocated to preserve what they call a near-pristine home for rare plants and wildlife, including the protected tortoise, the Western burrowing owl and bighorn sheep.

"It's actually a good project. It's just located in the wrong place," said Ileene Anderson of the Center for Biological Diversity, a Tucson, Ariz.-based environmental group.

The dispute is likely to echo for years as more companies seek to develop solar, wind and geothermal plants on land treasured by environmentalists who also support the growth of alternative energy. In an area of stark beauty, the question will be what is worth preserving and at what cost as California pushes to generate one-third of its electricity from renewable sources by 2020.