(CNN) -- Half a million acres will be protected Wednesday when President Barack Obama establishes the Organ Mountains-Desert Peaks National Monument.
It's "a once-in-a-lifetime opportunity" to head off development on the swath of land in south-central New Mexico that has "unique Pre-American, New Mexican, and American history," the monument's official website says.
For Obama, signing a proclamation Wednesday at the Department of the Interior will bring to fruition a promise in his 2014 State of the Union address: "I'll use my authority to protect more of our pristine federal lands for future generations."
White House spokesman Jay Carney said, "By establishing the monument, the President will permanently protect more than 496,000 acres to preserve the prehistoric, historic and scientific values of the area for the benefit of all Americans."
Carney cited an independent study that found the monument could generate $7.4 million "in new economic activity annually from new visitors and business opportunities, while preserving access for sportsmen, ranchers and recreational users."
The monument is apparently smaller than what some in New Mexico had sought. A proposal had called for 600,000 acres to be protected, according to the website.
The United States has 77 other national monuments, according to the organization National Park Advocates, which operates nationalparkstraveler.com. Some were created by acts of Congress; others by presidential proclamation.
The Bureau of Land Management operates 19 national monuments across nine Western states, including Arizona, California, Colorado, Idaho, Montana, New Mexico, Oregon, Utah and Washington.
In October 2012, Obama established the Cesar E. Chavez National Monument in California.