After seven years of study and public comments, the National Park Service (NPS) is recommending the urban foothills of the San Gabriel Mountains and part of the Rio Hondo and San Gabriel river corridors join the Santa Monica National Recreation Area (SMMNRA).

It would expand the national recreation area — which currently stretches from the Oxnard Plain, Topanga Canyon, Malibu Creek to the Hollywood Hills at Griffith Park — to include a “San Gabriel Unit.” That would add about 49,000 acres — 37 percent of which is already protected by the Angeles National Forest — to the SMNRA, the largest urban national park in the world.

The half-mile river corridor around the San Gabriel and Rio Hondo rivers would stretch from the border of the Angeles National Forest south to Santa Fe Springs. The "San Gabriel Unit" would also include portions of the western Puente Hills "with ecological resource value and recreational potential."

Though the area lies in heavily-populated suburbs of the San Gabriel Valley and eastern Los Angeles, the NPS study concluded that the region’s ecosystems are nationally significant. The region provides habitat to numerous rare and threatened plant and wildlife species, like the coastal sage shrub, one of the most endangered plant groups in the state.

“The San Gabriel Mountains are among the fastest growing mountains in the world,” the study said. “Forces from the San Andreas Fault to the north and a series of thrust faults on their south face are causing the San Gabriel Mountains to rise as much as 2 inches a year.”

Protecting and improving the lower Rio Hondo and San Gabriel River regions, home to a string of parks and two bicycle trails, has been a focus of local recreation groups. Last week, the Altadena-based Amigos de los Rios group announced it had secured funding for several projects at El Monte’s Peck Road Water Conservation Park, Pico Riviera's Rio Vista Park, Whittier Narrows Recreation Area and other parks that lie along the concrete-banked rivers as a part of what they call the Emerald Necklace Vision Plan.

Environmentalists have sued the U.S. Forest Service in years past for failing to protect the habitats of sensitive animals and plants in the area. The new protections could bring the agency more resources.

Congress must vote on the proposed changes to authorize the plans.

This story has been clarified to note that the National Park Service proposal refers to the foothills of the San Gabriel Mountains and not the entire mountain range.