Union officials, power industry executives, regulators and some environmentalists have also expressed concern about the impact of the monument legislation, but few would speak publicly for fear of antagonizing one of California’s most powerful politicians.

Image David Myers, executive director of the Wildlands Conservancy, and Sierra, his dog. Credit... Ann Johansson for The New York Times

The debate over the monument encapsulates a rising tension between two goals held by environmental groups: preservation of wild lands and ambitious efforts to combat global warming.

Not only is the desert land some of the sunniest in the country, and thus suitable for large-scale power production, it is also some of the most scenic territory in the West. The Mojave lands have sweeping vistas of an ancient landscape that is home to desert tortoises, bighorn sheep, fringe-toed lizards and other rare animals and plants.

As conflicts over building solar farms in the Mojave escalated earlier this year, Mrs. Feinstein trekked to the desert in April. The senator’s caravan, including the heads of two of the nation’s largest utilities, top energy regulators and a group of environmentalists, bumped along a dirt track and pulled up to a wind-whipped tent. Inside, executives with a Goldman Sachs-owned developer waited to make their case for building two multibillion-dollar solar power plants.

The presentation over, the entourage rolled on to the next solar project site to hear the developer’s pitch. Mrs. Feinstein gave the developers a hearing but was not moved by their arguments, according to five people present on the tour. The senator seemed concerned about the visual effect of huge solar farms on Route 66, the highway that runs through the Mojave, they said.

“When we attended the onsite desert meeting with Senator Feinstein, it was clear she was very serious about this,” said Gary Palo, vice president for development with Cogentrix Energy, a solar developer owned by Goldman Sachs. “It would make no sense for us politically or practically to go forward with those projects.”