Nonnative plants include pepper trees, tobacco trees, and mustard. There are no creeks, except for ephemeral freshets after storms, and no native riparian species such as oaks. Mature eucalyptus trees and some pine trees grow along some of the fence lines, where the area abuts housing tracts and the city's trail system. The area has been modified by large earth-moving projects to reduce the number of steep hills and canyons, allowing Gilbert Street to be constructed and real estate developments and later a golf course to be built on the west side of Gilbert. East of Gilbert Street, the undeveloped area consists mainly of a large, sun-exposed, gentle north-facing slope. The larger area west of Gilbert contains rugged terrain, predominantly south-facing slopes, and a large, long, dry, flat-bottomed canyon that runs north-south. The canyon bottom has been paved, and provides a fire road accessible from the nearby fire station on Rosecrans Avenue. The steep sides of the canyon were terraced and networked with asphalt roads for oil drilling. Impressive cliffs are a landmark visible to motorists on Rosecrans Avenue. U.S. Geological Survey researchers have found invertebrate fossils representing 184 taxa from 158 localities in the "San Pedro" Formation in the Coyote Hills, including various species of annelids, mollusks, arthropods, and echinoids; the fossils suggest a late Pliocene to early Pleistocene age for outcrops of the formation. The occurrence of the bivalve "Solamen columbianum" in the area marks its first occurrence as a fossil. The oldest fossil occurrence of the gastropods "Tegula pulligo" (Gmelin), questionably "Haliotis cracherodii", and the crustacean "Randallia ornata" occur in the "San Pedro" Formation in the Coyote Hills. A brush fire, the Risner fire, originated at a transient encampment in the area. It burned about 80 acres on September 8 and 9, 2015, prompting the evacuation of about 40 nearby homes.