Past and present land-use and other human caused events have also resulted in changes in the vegetation. Poly Canyon is home to a great diversity of plants, animals, plant communities, and wildlife habitats. Many of these plant and animal species and their habitats are sensitive and must be protected. Several of these species are listed as rare, threatened, or endangered species. Soils and geology on the site, like the vegetation, are complex and form a mosaic pattern that often corresponds with vegetation patterning.
Geological formations range from sandstone-shale complex to serpentinite.
Soils range from fine textured soils in some of the floodplain and grassland areas to rocky soils on the steep hillsides covered by coastal scrub and chaparral. The natural vegetation of the Poly Canyon is composed of a mosaic of grassland, coastal scrub, chaparral, coastal live oak woodland, and riparian woodland. The hillsides surrounding Poly Canyon are mostly a mosaic of rocky outcrops, coastal scrub, chaparral, and coastal live oak woodland although grassland dominates most of rolling hills especially in the eastern portion of the canyon. Blue gum eucalyptus, pepper trees, olive trees, and other exotics have been planted or have naturalized along portions of Poly Canyon near the campus and are mixed with the native vegetation. The photograph below, taken by Steve Marx and used with his permission, shows Poly Canyon and its watershed.