Glen Canyon's Fabulous Rock Formations
Glen Canyon Park is well known for its steep slopes and dramatic chert formations. These rock outcrops are Franciscan chert that formed over 200 million years ago from sediments made up of the shells of microscopic ocean-dwelling organisms called radiolaria, which settled to the ocean floor as they died. These layers of sediment were uplifted from the ocean floor by movement of the earth's crust, which also formed the hills of San Francisco.
Scarce water supply and shallow soils make the rock outcrops a challenging habitat for plant life; only well-adapted species survive. The powdery dudleya, Dudleya farinosa, has adapted to this dry environment by storing water in its basal rosette of succulent leaves. Crustose and foliose lichens offer us another example of plant adaptations; these lichens release special chemicals to obtain nutrients from the rock, a process that also contributes to erosion. Reptiles like the San Francisco alligator lizard, Gerrhonotus coeruleus, and the common garter snake, Thamnophis sirtalis, take advantage of the solar exposure the rock outcrops provide and spend many afternoons basking in the sun's rays.
Alligator lizard (Photo by Jon Campo)