The untended areas of Lake Perris may seem rocky and barren at first glance, but an amazing variety of natural wonders are waiting to be found by those who seek them out. The predominant plant community, coastal sage scrub, is home to a variety of birds and wildlife. Mule deer, roadrunners, bobcats, coyotes, cotton tail, jack rabbits, quail, gopher snakes, and rattlesnakes may sometimes be seen by day, though they tend to shy away from people. More frequently seen are a wide variety of lizards, rodents, water fowl, and birds of prey. Beautiful displays of wildflowers occur during the rainy season- generally November through April.
Lake Perris is ringed by various hills and small mountains. The coastal sage scrub community is predominant on the south-facing slopes of the Russell Mountains and Bernasconi Hills and is characterized by shrubby plants including desert encelia, brittlebush, sagebrush, black sage, white sage, buckwheat, and cacti. Conditions are somewhat shadier on hillsides that face north or northwest so that chaparral plants such as chamise, penstemon, and--caution!--poison oak are apt to be found. Remnants of the original perennial grasses that once flourished in this region can still be found in the flat interior of the park surrounding the lake, but the majority of plants that now make up the valley grassland community (including Russian thistle) were imported from Europe by early settlers. Riparian areas near springs and seeps, and on east and south lakes include willows, cattails, elderberry and nettles.