The Natural Area at O'Shaughnessy Hollow is dominated by scrub (67 percent) and grasslands (22 percent). Rock outcrops formations accounted for 10 percent of the Natural Area at O'Shaughnessy Hollow. Few tree- dominated areas exist in O'Shaughnessy Hollow. There are no developed areas within O'Shaughnessy Hollow. Forests dominate the fill slopes below O'Shaughnessy Boulevard, on the southwestern side of the canyon. Two small areas containing coast live oak, probably planted, occur near Islais Creek in the northern portion of the park.
O'Shaughnessy Hollow is owned by the San Francisco Recreation and Park Department.
44-O'Shaughnessy --O'Shaughnessy Blvd & Del Vale Ave.
O'Shaughnessy Boulevard separates the two Natural Areas with Glen Canyon Park to the east and O'Shaughnessy Hollow to the west. O'Shaughnessy is 3.6 acre Natural Area. Elevations in O'Shaughnessy Hollow range from approximately 325 to 550 feet above sea level, rising from south to north along the Boulevard and to the west rim of the canyon. The bottom of the canyon, where Islais Creek flows, is irregular but moderate in slope, dropping 350 feet over a distance of about 1 mile. The walls of the canyon are extremely steep, with many slopes approaching a length-to-height ratio of 1:1 (100 percent). Access to O'Shaughnessy Hollow is limited but possible by social trails from residential streets to the west, specifically DelVale Avenue. Recreational facilities in Glen Canyon Park include the Silver Tree Day Camp, a community recreation center, ball fields, playgrounds, a ropes course, and formal and informal trails. There are no developed areas within O'Shaughnessy Hollow. The diverse array of habitats and sensitive species combined with neighborhood interest and support of these parks, has made Glen Canyon Park and O'Shaughnessy Hollow extremely valuable to the people of San Francisco. Specific values associated with these Natural Areas include: high levels of recreational trail use; outstanding views; interpretive signs and ample opportunity for educational use; one of two last free-flowing creeks in the City; some of the City's largest and most impressive and accessible rock outcrops; excellent forage and nesting habitat for a variety of resident and migratory bird species; extensive grasslands providing habitat for butterflies and other insects; dense willow thickets offering protection for resident and migratory birds; red-tailed hawk and great-horned owl nesting sites and foraging areas; suitable habitat for special-status species of butterflies; important habitat for native plants; populations of sensitive plant and animal species; and extensive urban forest.