The president signed proclamations to protect Castner Range, a former military training and testing site in El Paso, and more than 500,000 acres around Avi Kwa Ame (ah-VEE-kwah-may), a sacred tribal site in southern Nevada, according to the White House.

The Washington Post reported in November that Biden would safeguard the vast expanse in Nevada using his authority under the 1906 Antiquities Act. It is the largest area protected so far in Biden’s presidency.

Biden, in an announcement at Interior Department headquarters, said the moves are part of the administration’s efforts to protect wildlife while slashing planet-warming emissions by preventing mining and oil drilling on public lands. They follow a flurry of conservation announcements from the White House in recent weeks, including one banning oil and gas leasing in U.S. waters in the Arctic Ocean.

“We’re protecting the heart and the soul of our national pride,” Biden said in a speech that drew repeated applause from a crowd of conservation advocates. “We’re protecting pieces of history and telling our story.”

The designations come as Biden faces intense criticism from environmentalists over the administration’s approval this month of a major oil drilling project in Alaska. In a sign of these tensions, climate activists outside the Interior Department protested the Willow oil project on Tuesday even as Biden announced the new national monuments at a conservation summit with tribal leaders inside the building.

The Fort Mojave and 11 other tribes consider Avi Kwa Ame a central part of their creation story and the site from which their ancestors emerged. Environmental groups also have supported the designation, saying it will help preserve critical habitat for the desert tortoise and other species.

The proclamation will render about 507,000 acres — spanning almost the entire triangle at the bottom of the Nevada map — off-limits to mining and other kinds of development. It also will prevent renewable energy projects from breaking ground there, although administration officials have argued that the monument will not undermine Biden’s clean-energy agenda.

Interior Department officials said Tuesday that the designation does not block the construction and maintenance of utility, water and telecommunications facilities, or pipelines, roads and highways.

Tribal government leaders and local advocates from the Honor Avi Kwa Ame coalition, which pushed for the designation, traveled to Washington for the announcement.

“We are overjoyed,” the group said in a statement. “The president’s action today will safeguard hundreds of thousands of acres of cultural sites, desert habitats, and natural resources in southern Nevada, which bear great cultural, ecological, and economic significance to our state.”

Outside the national monument’s boundaries, Interior’s Bureau of Land Management has identified more than 9 million acres of land in the state for potential large-scale solar development and, separately, 16.8 million acres for possible wind-energy projects. Federal officials also have designated more than three-quarters of the monument area as either wilderness or “areas of critical environmental concern.” Biden said the designation will tie together one of the country’s largest contiguous wildlife corridors.

“Breathtaking deserts, valleys, mountain ranges, rich in biodiversity, sacred lands that are central to the creation story of so many tribes that have been here since time immemorial,” he added, describing the region. “It’s a place of reverence, it’s a place of spirituality, it’s a place of healing. And now it’ll be recognized for the significance it holds and be preserved forever. Forever.”

The Castner Range National Monument will encompass 6,672 acres that the U.S. Army used for training and testing during World War II, the Korean War and the Vietnam War. The Army stopped training at the site in 1966, at which point it was closed to the public because of unexploded ordnance.

The Defense Department, which manages Castner Range, has been studying the feasibility of cleaning up the site under the nation’s Superfund law. The department will continue to manage the national monument and will help clean up the site until it is safe for public access.

While Castner Range is off-limits to people, it provides habitat for an array of wildlife, including the American peregrine falcon, the golden eagle, the black-tailed prairie dog and the Texas horned lizard. The endangered Sneed’s pincushion cactus and other rare plants also grow in the area. In addition, the range contains archaeological artifacts from early Native American settlements, including rock art and pottery.

Local advocates said the designation shows respect for locals and Indigenous people and will ensure access to the outdoors for low-income communities. People from El Paso and the wider region have been fighting for the designation for 52 years, according to the Frontera Land Alliance.

“The challenges that our city has faced — poverty, pollution, inequality, climate change — are the results of broken relationships,” Moses Borjas, pastor of Living Covenant Church in El Paso and a conservation advocate, said in a statement. “The designation of Castner Range as a National Monument adds to the healing process that our city needs in these times. Protecting Castner Range is not only protecting our mountains and wildlife, but it’s protecting our history, heritage and our legacy.”

Biden had previously suggested he would travel to southern Nevada to designate Avi Kwa Ame. But scheduling difficulties have prevented the president and Nevada’s congressional delegation from traveling to the state for a ceremony there. Aides in recent weeks began exploring whether to hold a ceremony in Washington to better accommodate lawmakers’ schedules.

Written by Maxine Joselow and Timothy Puko for The Washington Post.