Red Hills (Tuolumne County)  The Red Hills are a mountain range in Tuolumne County, California. Elevations within the Red Hills vary between 750 and 1,750 feet above sea level. Slopes of the hills themselves vary from about 30% to 75%. In 1937 Paramount filmed on location at the Red Hills area the motion picture "North of the Rio Grande" (1937) starring William Boyd as 'Hopalong Cassidy'. The studio sent a Hetch Hetchy railroad locomotive No.30 to roll through the Red Hills scenic landscape. The Red Hills contain The Red Hills of Tuolumne County Area of Critical Environmental Concern, managed by the Bureau of Land Management as an Area of Critical Environmental Concern. The Red Hills Management Area consists of 7,100 acres (slightly more than 11 square miles) of public land located near the intersection of California State Route 49 and California State Route 120, just south of the historic town of Chinese Camp, California in Tuolumne County. The entire Red Hills Management Area has been designated as an Area of Critical Environmental Concern. The purpose of the designation is to protect the rare plant species found there, the unusual serpentine soils that provide habitat for unique flora of the area, habitat for the rare minnow known as the Red Hills roach and to protect bald eagle wintering habitat. The Red Hills Management Area is located within the western tectonic block of the Sierra Nevada metamorphic belt. Within this block are Upper Jurassic volcanic and sedimentary rocks of island arc derivation which were highly deformed and weakly metamorphosed during the Nevada orogeny. These rocks were then intruded by plutons associated with the emplacement of the Sierra Nevada batholith, east of the metamorphic belt. The Management Area includes much of the Tuolumne ultramafic complex, one of the largest exposures of serpentine rocks in the Sierra Nevada metamorphic belt. Nearly the entire area is underlain by dunite, a variety of peridotite consisting of dark green olivine and minor chromite, which has been partly or entirely serpentinized to antigorite magnesite-magnetite. The dunite intruded into andesite pillow breccias and flows of the Peñon Blanco volcanic formation, which crops out near the northeast and southern boundaries of the Management Area. The intrusion of ultramafic material occurred along crustal weaknesses associated with the Bear Mountain fault, a northwestward trending thrust fault that dips steeply to the northeast, and has over 10,000 feet of vertical displacement.