Gregory Korte

USA TODAY

President Obama designated the San Gabriel Mountains outside of Los Angeles as a national monument Friday, setting aside 346,177 acres of national forest as a recreational area.

Using his authority under a 108-year-old law, Obama's executive action will permanently protect the forest from development and set it aside as an outdoor recreation destination.

Against a picture-perfect mountain scene, Obama extolled the forest for its "rugged slopes and remote canyons," wild lilacs and mountain mahogany trees.

"But it's not just the natural beauty of the San Gabriels that makes it invaluable. Within these hills lies millennia of history." he said. The forest is home to Native American rock art Mount Wilson Observatory, where astronomy Edwin Hubbell discovered that the universe was still expanding.

The move is not without controversy. Some park neighbors worry about what the move would mean for fire suppression efforts and restrictions on hunting and off-road vehicles.

"This place is special and must remain special," said Agriculture Secretary Tom Vilsack, who oversees the U.S. Forest Service.But cities in the region applaud the designation, saying the mountains are an important source of the region's fresh water, clean air and open space. "Designating the area as a National Monument will ensure its resources are managed properly and protected for future generations to enjoy," Los Angeles Mayor Eric Garcetti said in a statement.

The San Gabriel Mountains National Monument is the 177th such designation since President Theodore Roosevelt signed the Antiquities Act in 1906. Obama has established or expanded 13 of them, all but one of them without congressional approval.

"And I'm not finished," Obama said, hinting that he was actively considering additional national monuments.

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