Black Mountain Open Space Park, Nature reserve in Rancho Peñasquitos, San Diego, United States

Black Mountain Open Space Park covers 2,352 acres in the Black Mountain Ranch and Rancho Peñasquitos areas of northern San Diego. Its central feature is Black Mountain, a 1,554-foot peak of the Santiago Peak Volcanics with communication towers at the top. Chaparral grows on the east and north sides, coastal sage scrub on the south and west.

The Kumeyaay lived on Black Mountain before European contact and called it "Amat Kwanyil". In the 1920s, Escondido rancher and rodeo cowboy Frank Hopkins opened an arsenic mine in the canyon to supply white arsenic for pesticides against boll weevils; it was abandoned in 1927. In 2016, soil sampling by the University of San Diego found high arsenic levels near the mine, and in January 2017 the San Diego City Attorney recommended closing lower trail sections.

The Kumeyaay, who lived on the mountain before European contact, called it "Amat Kwanyil". The Jas Arnold Trail for All People, at the Miner's Ridge Loop parking lot, is a handicapped-accessible path named for the park advisory committee's long-serving chair, who died in May 2016.

The Miner's Ridge Loop Trail runs 2.3 miles with 670 feet of climbing and is reached from Carmel Valley Road; the Nighthawk Trail starts from Hilltop Community Park. The Jas Arnold Trail for All People, at the Miner's Ridge Loop parking lot, is wheelchair-accessible, and the Lilac Canyon Trail links that lot to the Glider Port. Lower Miner's Ridge sections were recommended for closure in 2017 after arsenic was found in soil samples.

Black Mountain is an extinct volcano that last erupted 118–125 million years ago, part of the Santiago Peak Volcanics, a chain of volcanic islands formed about 150 million years ago. The Kumeyaay, who lived on the mountain before European contact, called it "Amat Kwanyil".