The Santa Rosa range, its peaks and canyons, were all formed by igneous and metamorphic rock moving between two major tectonic zones, the San Andreas and San Jacinto Faults. Spring-fed streams run through the steep canyons and support fan palm oases that sometimes appear seemingly out of nowhere. Part of the Peninsular Ranges that connect Southern California to Baja, the range and faults all trend northwest-southeast, meaning you're heading inland the further south you travel.
The native rare plants of the wilderness in this area are incredibly diverse and fascinatingly named, from Nuttall's scrub oak to the triple-ribbed milkvetch, beavertail cactus, fishhook cactus, Orcutt aster, desert woolstar, apricot mallow, and the pink-blooming cheesebush. The range is known for its wildflowers and flowering cactus, as well as brightly colored trees like the palo verdes and desert willow. If your goal is to see incredible blooming flowers, check your weather advisory: A dry summer means less flowers and perennials to enjoy, although desert mainstays such as the tall ocotillo and sturdy pinon pine, and many types of yucca and cholla cactus, are fairly reliable bloomers.
In terms of fauna, there are mule deer, coyote and bobcat throughout, as well as quail and dove, golden eagles, kit foxes, iguanas, chuckwallas and the red diamond rattlesnake. Several species of jackrabbit appear at dawn and dusk, as well as meat-eating roadrunners looking for lizards and snakes and mice. But most conversation -- if not sightings -- tends to focus on the Peninsular Bighorn Sheep.
The Range is a protected habitat for these endangered animals, with a stable population of only about 30 adults, with a total population of roughly 800 sheep, ranging down out of the Santa Rosas. Peninsular Bighorn Sheep tend to roam the range between a 1,000 and 4,000 feet (304 and 1219 meters) in elevation. The Bear Creek, Deep Canyon and Martinez Canyon oases are important locations in the summer for Bighorn reproduction, and you can sometimes spot sheep on the slopes, in the rocks just above the desert floor [source: Bighorn Institute].