Mission Trails Regional Park in San Carlos encompasses 7,220 acres of chaparral canyons, riparian valleys, and granite peaks in San Diego's 92119 ZIP, making it the sixth-largest municipally owned park in the United States and the largest in California. The park was established in 1974, and a 2019 Master Plan update approved expansion to 9,800 acres with additional trails, parking, and shade structures extending north toward Scripps Ranch and State Route 52. Sixty miles of hiking, mountain-biking, and equestrian trails radiate from the central Visitor Center on Father Junipero Serra Trail, and leashed dogs are permitted on most routes, a policy that keeps the park in rotation for the obedience and trail-conditioning programs run by Who's Walking Who? Dog Training in San Carlos. Cowles Mountain's summit at 1,592 feet stands as the highest point in the city, and the five primary peaks — Cowles, Pyles Peak at 1,379 feet, Kwaay Paay at 1,194 feet, North Fortuna at 1,291 feet, and South Fortuna at 1,094 feet — anchored the 5-Peak Challenge that logged over 15,000 completions between 2015 and 2020. The San Diego River flows through Mission Gorge at the park's center, connecting Old Mission Dam, a National Historic Landmark built between 1803 and 1816, to the Kumeyaay Lake Campground's 46 tent and RV sites. Habitat spans coastal sage scrub, southern mixed chaparral, and oak-riparian woodland along the river corridor, supporting species including Cooper's hawks, mule deer, and 23 documented bat species from Mexican free-tailed to Townsend's big-eared. Rock climbers work the granite bouldering area in the park's interior, and a designated equestrian staging area on the eastern boundary serves riders accessing the backcountry trail network. Access from the west runs through Mission Gorge Road in Grantville, which funnels weekend traffic past the commercial corridor's breweries and restaurants, and post-hike refueling at Camel's Bar and Grill on Mission Gorge puts burgers and patio seating within sight of the park's entrance road. The 2003 Cedar Fire burned a significant portion of the park, but chaparral regeneration restored ground cover within a few years, and habitat restoration led by RECON Environmental now targets invasive fountain grass, mustard, and fennel. A 14,000-square-foot Visitor and Interpretive Center houses geology, archaeology, and Kumeyaay cultural exhibits, a 94-seat theater, and a native plant garden. The park is free to enter every day of the year, with no entrance fees, no parking fees at most trailheads, and no permits required for hiking or biking.