President Obama recently set aside 346,177 acres of the California's San Gabriel Mountains as a national monument, "permanently protecting the popular outdoor recreation destination to increase access and outdoor opportunities for the area's residents." 

The newly designated San Gabriel National Monument encompasses about half of the Angeles National Forest, the closest — and in many cases, the only — access to open space for many of the residents of Los Angeles County. About 17 million people live within a 90-minute drive of the San Gabriels, many of whom have no other access to wilderness or outdoor recreation areas. Another key feature of the newly protected area is that the mountains provide one-third of the populated areas’s clean water supply. 

The San Gabriel Mountains are also a high-quality wilderness area, providing habitat for rare and endangered animals like the California condor, and a rich array of cultural and historical features, according to a White House news release.

The monument area includes Mount Wilson Observatory where Edwin Hubble discovered galaxies beyond the Milky Way and Albert Michelson provided the first modern measurement of the speed of light, as well as the Aliso-Arrastre Special Interest Area, which features rock art and Native American cupules.

Here's a look at what the new San Gabriel National Monument area will encompass:

San Gabriel Mountains map

Obama created the new national monument using his authority under the Antiquities Act of 1906, a bill signed by Teddy Roosevelt that allows any U.S. president to set aside “objects of historic or scientific interest that are situated upon the lands owned or controlled by the Government of the United States to be national monuments.” The current president has used this authority to create 12 other national monuments, including the San Juan Islands National Monument in Washington state, and the offshore Pacific Remote Islands Marine National Monument, making it the largest marine reserve in the world.

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Obama designates new national monument
The new San Gabriel National Monument is the only accessible open space for many of Los Angeles County's 17 million residents.