The upper reaches and headwaters of Santa Rosa Creek are on Hood Mountain on the western slopes of the southern Mayacamas Mountains. Much of the ecosystem of the headwaters is relatively dense mixed oak woodland, which has a canopy of coast live oak, Douglas fir, California buckeye (Aesculus californica) and bigleaf maple. In these oak woodlands, the dominant understory plants are toyon, blackberry, western poison-oak and in occasional drier patches some coyote brush. In some of the steeper, cooler riparian zones there are a high concentration of California bay laurel. Common animals observed include California mule deer, gray squirrel, raccoon, skunk, Western pond turtle, river otter and opossum. Less frequently tiger salamander, bobcat and mountain lion are seen. There is abundant birdlife including the scrub jay, Steller's jay, acorn woodpecker and junco.