In the peaks of Diamond Heights in western San Francisco sits Glen Canyon, which hosts varied habitats that existed in the area before development occurred throughout the city. The canyon occupies 70 acres and is open to the public. According to BayNature.org, "Glen Canyon contains one of the few stretches of historic free-flowing Islais Creek. Good for a pleasant stroll or outing with the dog, the park also hosts a community center, sports fields, children's camp, and tennis courts."
Fun little hike in the city without a full day's commitment. Some great areas meandering along Islais Creek and also great views of the canyon itself when the trail winds out from the canyon floor to the edges and boulders up top. Popular with dog walkers and people of all ages.