The East Bay Regional Park District calls Diablo Foothills an "imposing gateway" to Mount Diablo State Park and the Walnut Creek Open Space. The 1,060-acre park lies at the western edge of the mountain. It borders Castle Rock Recreation Area to the east and Shell Ridge Open Space to the north, and Wikipedia says the three together offer about 18,000 acres of parkland.
Castle Rock and the falcons
The park's best-known sight is the group of sandstone formations in Pine Canyon called Castle Rock. The rocks themselves are in Mount Diablo State Park, but most visitors reach them through Diablo Foothills. Every year the formations close from Feb. 1 to Aug. 1 to protect nesting peregrine falcons, which are highly territorial and easily disturbed during nesting season. The rest of the park stays open.
What you'll see
Grassland and oak savanna cover the hills, with creekside and oak woodland in the valley. Pine Creek runs through Pine Canyon in the eastern part of the Walnut Creek watershed. The park district lists mule deer, bobcats, coyotes, gray foxes and long-tailed weasels among the mammals, and California quail, scrub jays and brown towhees among the nesting birds. Year-round pools in Pine Creek hold green sunfish, mosquitofish and largemouth bass.
Castle Rock Recreation Area
Castle Rock Recreation Area, in an oak-shaded canyon along Pine Creek, has long hosted large group picnics of 300 people or more. Some picnic areas can be reserved, and others are first come, first served. The Castle Rock Pool Complex has a 30-by-70-foot pool, but it is closed and will reopen for the 2027 swim season.
Parking and hours
The northern staging area is at 1700 Castle Rock Road in Walnut Creek. Parking is free. From November through February the lot is open 7:30 a.m. to 7 p.m., and the park itself is open 5 a.m. to 10 p.m. The kiosk is cashless.
Up the mountain: our Mount Diablo State Park guide.