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Washington • President Barack Obama will create the largest national monument of his tenure on Wednesday, making nearly 500,000 acres of southern New Mexico off limits to development.

The Organ Mountains-Desert Peaks region has petroglyphs from three American Indian societies in its canyons, as well as desert grasslands and a petrified forest. The area is twice as big as the Rio Grande del Norte National Monument in New Mexico, which previously held the ranking as Obama's largest.

Many community leaders had pressed the president to protect the region under the Antiquities Act rather than waiting for Congress to make a move. But some in the area near Las Cruces, including cattle ranchers and Republican lawmakers, oppose a presidential designation, saying it is too far-reaching and will not provide enough safeguards for border officers.

White House press secretary Jay Carney said Monday that Obama is working "to preserve the prehistoric, historic and scientific values of the area for all Americans," and that the monument will encourage tourism.

Carney said Wednesday's designation — which Obama will sign at the Interior Department — is part of a week-long effort aimed at "helping businesses invest here in America" to spur job development.

Sen. Martin Heinrich, D-N.M., who had pressed for the designation, said in a phone interview that it reflects the hard work of local advocates.

"Anytime you have a recognition of that work that reaches all the way to the White House, that's pretty special," he said.

But Rep. Rob Bishop, R-Utah, chairman of the House Natural Resources subcommittee on public lands and environmental regulation, sent a letter to Obama on Monday urging him not to designate the new monument on the grounds that there are not sufficient safeguards for U.S. Customs and Border Protection operations. He cited an attack on a National Park Service employee at Arizona's Chiricahua National Monument last year at the hands of drug smugglers.

Mike Matz of the Pew Environment Group said the president's actions could spur Congress to protect more land.

"True to his word, President Obama is going to use the authority granted to him by Congress to protect a lasting legacy of America's natural heritage for future generations," he said in an email. "We hope this is a portent of further action to conserve land by his administration and by Congress."

Heinrich said he and other lawmakers will continue to work on legislation to address outstanding issues, including a buffer zone for border patrol operations and strengthened wilderness protections.