Castle Rock State Park, State park in the Santa Cruz Mountains, California, US

Castle Rock State Park covers 5,242 acres along the crest of the Santa Cruz Mountains, almost entirely in Santa Cruz County. Its steep canyons hold unusual sandstone formations, including the namesake Castle Rock, and forests of coast redwood, Douglas fir, and madrone left largely wild. A 32-mile trail network crosses the park.

Castle Rock State Park was established in 1968. In 2011, California Assembly Bill 42 allowed state parks to enter operating agreements with nonprofits, and the Portola and Castle Rock Foundation was formed. On March 14, 2012, a $250,000 donation from the Sempervirens Fund removed the park from the closure list for one year. A new entrance with 90 parking spaces opened on August 1, 2019, funded by an $8.7 million donation from the Sempervirens Fund.

The park takes its name from Castle Rock, a sandstone formation that gives the park its name and draws rock climbers to its faces. The 32 miles of trails connect with a wider network reaching Big Basin Redwoods State Park and the Pacific Coast. Two walk-in campgrounds let backpackers stay overnight among the redwoods and Douglas firs.

The entrance is on California State Route 35 (Skyline Boulevard), 2.6 miles southeast of the junction with State Route 9, next to Sanborn County Park. The 32 miles of trails link to Big Basin Redwoods State Park and the Pacific Coast. Dogs are barred from trails and campgrounds; horses only on designated trails.

The park's 32 miles of trails connect to a larger network linking the Santa Clara and San Lorenzo valleys with Big Basin Redwoods State Park and the Pacific Coast. Its overnight parking lot makes it a common starting point for the 30-mile Skyline-to-the-Sea Trail, which begins nearby at Saratoga Gap and ends at Waddell Beach north of Santa Cruz.