Diversity is perhaps the most important feature of the vegetation found within Chino Hills State Park. In fact, Chino Hills has several different kinds of vegetation in each of its major habitats.
In the park’s creek zones, cattail stands provide habitat for a variety of wildlife, among them red-winged blackbirds. Along seasonal and year-round creeks, the willow and sycamore woodlands have understories of wild rose, stinging nettle and mule fat. These riparian areas provide cover and food for numerous animals and nesting birds. Many of these nesting birds are migratory species that come to the streamside habitats from Central and South America each spring to raise their young. Southern California black walnut trees join coast live oaks to form woodlands above the creeks, often on north facing slopes. These walnut woodlands are another important and rare plant community preserved in the park. Only a few thousand acres of this California habitat still exist, with about one thousand acres in preserves. Several hundred acres are protected at Chino Hills State Park.
The Tecate cypress is another special type of plant community found only in a few places in the United States. Several Tecate cypresses are found in Coal Canyon, adjacent to the larger ecological reserve managed by the California Department of Fish and Game.
Several different scrub and chaparral communities along the hills and slopes above the canyon floors include coastal sage scrub, California sagebrush, California buckwheat and purple sage, as well as a mixed chaparral community dominated by laurel sumac and toyon. Many California wildlife species depend on these scrub and chaparral communities for survival. Because these communities are disappearing as urban development continues, they form an increasingly important part of the biological resources protected in the park.
Most of the grassland in the park is non-native annual European grasses that were introduced here during the early ranching years. However, grassland species native to California, such as purple needle grass and giant rye can be found among the annuals. An active grassland restoration program in the park is restoring native grassland to its more natural and dominant state.