The park and hollow offer an experience of San Francisco's diverse terrains as they appeared before the intense development of the region in the late 19th and the 20th centuries. The park incorporates free-flowing Islais Creek and the associated riparian habitat, an extensive grassland with adjoining trees that supports breeding pairs of red-tailed hawks and great horned owls, striking rock outcrops, and arid patches covered by "coastal scrub" plant communities. In all, about of the park and hollow are designated as undeveloped "Natural Area". Elevations in Glen Canyon Park range from approximately 225 feet (69 m) above sea level at the south end of the park to 575 feet (175 m) above sea level at the north end and along the eastern rim of the canyon; the walls of the canyon are extremely steep, with many slopes approaching a length-to-height ratio of 1:1 (100 percent).