San Gabriel Mountains and Berryessa Snow Mountain national monuments to become larger. : President Joe Biden plans to expand the size of two national monuments in California later this month — one in the San Gabriel Mountains east of Los Angeles and the other in remote landscapes north of Napa Wine Country. The Washington Post, CNN and the New York Times quoted unnamed White House officials late Thursday and Friday morning saying that Biden will sign a declaration expanding the 346,177-acre San Gabriel Mountains National Monument in Southern California by 110,000 acres within the next few weeks.