Walk past the ball field and tennis courts at Elk and Chenery streets and the city falls away. Glen Canyon Park is a steep-walled canyon in the middle of San Francisco, between Glen Park, Diamond Heights and Miraloma Park. It has a running creek, red rock outcrops and grassland where hawks and owls nest.
Islais Creek and the trails
Rec and Park calls Islais Creek one of the few free-flowing creeks left in San Francisco. Willows, horsetails, seep monkeyflower and red columbine grow along the creek, and some of the birds that feed there migrate from as far as South America. A 3.7-mile trail network runs from the creekside up the canyon's steep eastern slope, and the Creeks to Peaks trail picks up from the Islais Creek trail to show off the canyon's different ecosystems.
The grassland is golden in fall. By February the hills turn green, and spring brings California poppies, blue-eyed grass, checkerbloom and mule's ears. Farther north, coastal scrub of coyote brush, sage and California blackberry shelters ground-nesting birds. Rec and Park says coyote brush alone supports more than 250 insect species.
Enter at the southeast corner at the end of Bosworth Street, down the wooden stairway at Sussex Street, or on trails from the Diamond Heights Shopping Center.
Rocks and climbers
The canyon's red, banded rock is Franciscan chert. It formed from the remains of tiny ocean organisms on the deep sea floor near the equator and was carried to California on the moving ocean plate. Local climbers consider the park one of the best bouldering spots near San Francisco.
Dynamite, dairies and a mini-zoo
Adolph Sutro bought land in the canyon in the 1850s and called it his 'Gum Tree Ranch' for the blue gum eucalyptus he planted. On March 19, 1868, the Giant Powder Company began making dynamite here under a license from Alfred Nobel. It was the first commercial dynamite production in the United States. On Nov. 26, 1869, an explosion destroyed the plant, killing two people. The site is California Historical Landmark No. 1002, and a plaque was placed in 2017.
A dairy operated in the canyon into the 1920s. After the Crocker Real Estate Company bought the land in 1889, it added an aviary, a small zoo and balloon rides, then ran the canyon as a rented picnic ground. Rec and Park says the canyon also served as a refugee camp after the 1906 earthquake. The city bought it in 1922. The WPA built the recreation center in 1937. In 1958 the state proposed a crosstown freeway through the canyon along O'Shaughnessy Boulevard, but neighborhood groups opposed it and the plan was abandoned.