President Barack Obama created a new national monument on Wednesday, setting aside a half-million acres of federal land in southern New Mexico where Geronimo once roamed.

The Organ Mountain-Desert Peak region, which lies between El Paso, Texas, and Las Cruces, New Mexico, is the second national monument the president has designated this year. At 500,000 acres, it is the 11th of his presidency and the largest.

In March, Obama added 1,600 acres to the California Coastal National Monument to include the Point Arena-Stornetta region 129 miles north of San Francisco.

"Anyone who has ever seen the Organ Mountains that overlook Las Cruces will tell you they are a spectacular site," Obama said at a White House ceremony.

Half of the new monument is designated as wilderness, closing it to cars and development such as mining. As the new monument occupies land managed by the federal Bureau of Land Management, the agency will continue to oversee it. (Related: "Climate Change Threatens National Monuments.")

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Roosevelt's Legacy

Obama has created his new national monuments using the 1906 Antiquities Act, authored by President Theodore Roosevelt, which protects cultural and scientific resources on federal land. All presidents except Richard Nixon, Ronald Reagan, and George H. W. Bush have used the act to set aside sites such as the Statue of Liberty, the Grand Canyon, and the Grand Tetons, according to an Interior Department spokesperson.

The establishment of newly protected federal land was hailed by environmentalists such as the Wilderness Society, but opposed by western Republican lawmakers who have long characterized such designations as "seizures" to lock up federal land, placing it out of reach of development.

Last month, for example, the Republican-controlled U.S. House of Representatives voted along party lines to limit the president's power to establish national monuments. The bill is not expected to come to a vote in the Democrat-controlled Senate.

Obama chided his congressional opponents by noting that he has preserved more than three million acres of public lands. "And I'm not finished," he said. "I'm searching for more opportunities to preserve federal lands where communities are speaking up. Because wherever I get an opening to get things done for the American people, I'm going to take it."

Mountain Hideout

The Organ Mountains-Desert Peaks monument encompasses five mountain ranges with spire-like peaks that resemble the pipes of an organ. The region has some 243 known archeological sites, including some of the earliest known Native American villages, as well as ancient petroglyphs drawn by three Native American tribes.

Apache warrior Geronimo and Billy the Kid, the 19th-century frontier outlaw, both used the mountains as hideouts, and Apollo astronauts trained on its rugged terrain. Pronghorn, mule deer, golden eagles, great-horned owls, and many other species make their homes in the mountains.

The monument was supported by New Mexico's U.S. senators Tom Udall and Martin Heinrich, both Democrats. But U.S. Representative Steve Pearce, a New Mexico Republican whose district includes part of the monument, introduced legislation last year to limit the size of the monument to 54,800 acres instead of 500,000 acres.

Dona Ana County Sheriff Todd Garrison told the Las Cruces Sun-News last month that the new status would prevent his deputies from having access to the land and inhibit their ability to patrol the area.

In an effort to neutralize opposition to the park, the website for the new Organ Mountain-Desert Peaks National Monument includes statements of support from local business leaders and a 2013 report prepared by the Las Cruces Green Chamber of Commerce that concludes the nation monument would contribute more than $7.4 million to the local economy, produce $560,000 in new taxes, and double the number of tourism and outdoor recreation jobs in the region.

U.S. Representative Rob Bishop, a Republican from Utah, has long campaigned against the creation of new national monuments and opposes several under consideration for Utah. In a letter to Obama, Bishop suggested that national monuments near the border provide cover for drug smugglers and human traffickers and "hamper the U.S. Border Patrol's ability to conduct routine patrols and apprehensions."

The U.S. Customs and Border Protection disputed that claim, saying the monument would "in no way limit" the agency's ability to patrol the border.