Covering 11,000 acres (4,500 ha), with 36 miles (58 km) of trails and unimproved roads, the park's boundaries stretch from Topanga Canyon to Pacific Palisades and Mulholland Drive.

In 1828 the Mexican Governor of Alta California granted Francisco Sepulveda provisional title to the more than 30,000 acres (12,000 ha) called Rancho San Vicente y Santa Monica.

Among the many homestead patents filed in the Santa Monica Mountains, the one filed by a beekeeper named McAtee was for the western edge of the Rancho San Vicente y Santa Monica, and area along what became Entrada Road, the current main entrance to Topanga State Park.

When Trippet died in 1923, his son, Oscar Jr., commissioned Los Angeles architect Summer Spaulding to build the superintendent's house, horse stables, and a skeet lodge.

[6][7][8] Businesses that remained included Cholada Thai, Malibu Feed Bin, Reel Inn, Topanga Ranch Motel, and Wylie’s Bait & Tackle Shop.

[14] Geologically, the park has many sedimentary sandstone rock formations, marine fossils, exposed faults, and volcanic intrusions.

The primary trailheads are at the Trippet Ranch area, including for the Musch Trail,[16] passing prominent Eagle Rock.

The Santa Inez Trail is accessible from Trippet Ranch on the west, or the Palisades Highlands neighborhood on the east.

The trail's lower section follows Santa Inez Creek through riparian habitats, and then climbs through unique and massive sandstone formations to the Topanga Fire Road and Trippet Ranch.

In protest, environmentalists and area residents collected more than 17,000 signatures asking that the closure idea be halted, with the petition delivered to the governor by a symbolic delegation of school children.

In July 2012, it was reported that nearly $54 million in "hidden" funds was in the possession of California's state park system, creating widespread anger.

In February 2013 it was revealed that the approximately $20 million had been hidden for as long as 20 years by the California Department of Parks and Recreation.

[18] In August 2012, Congressman Brad Sherman announced that he secured federal funds to help improve parks and public areas.

The Congressman said, "The Backbone Trail provides thousands of hikers, bicyclists and other outdoor enthusiasts with an unparalleled recreational experience through the heart of the Santa Monica Mountains.