and grasslands Mixed scrub Mountain mahogany scrubs High elevation meadows Other unvegetated areas Weather The semi-arid climate is characterized by low to moderate precipitation, great extremes in both daily and seasonal temperatures, and low relative humidity. Average annual precipitation is approximately at the lower elevations and in the highest areas. Average snow depths for higher elevations range between 35 and . Summers are hot and dry with occasional thunderstorms. Mountains The reserve is in the southern part of the Albion Mountains, bordered on the east by the Raft River valley and to the north by the Snake River valley. Elevations rise from where Circle Creek meets the reserve boundary to at the top of Graham Peak to the north. Soils The majority of the soils in the reserve are composed of grus, a coarse angular sand derived from the disintegration of the underlying granitic bedrock. They are highly erodible. Soil erosion is greatest near roads and on steep slopes and intermittent stream channels. Erosion in these areas has formed deep gullies. Some of the exposed soil banks are over high. Controversy Climbing on the Twin Sisters, a major geological formation in the Reserve, was banned following a National Park Service decision and later court case involving the Access Fund. The Access Fund asserted that the NPS decision was "arbitrary and capricious," while the NPS claimed that rock climbing on the Twin Sisters disrupted the "historic viewshed" of the California Trail. See also Oakley stone List of National Historic Landmarks in Idaho List of National Natural Landmarks in Idaho National Parks in Idaho National Register of Historic Places listings in Cassia County, Idaho References Etched in Stone: the Geology of City of Rocks National Reserve and Castle Rocks State Park (review) Almo Creek Geologic Map and Digital Data Base of the Almo Quadrangle and City of Rocks National Reserve, Cassia County, Idaho External links City of Rocks National Reserve National Park Service City of Rocks National Reserve Map National Park Service City of Rocks National Reserve Idaho Department of Parks and Recreation City of Rocks National Reserve Location Map Idaho Department of Parks and Recreation An entry by the International Dark-Sky Association California Trail Climbing areas of the United States Landforms of Cassia County, Idaho National Historic Landmarks in Idaho National Natural Landmarks in Idaho National Park Service areas in Idaho National Register of Historic Places in Cassia County, Idaho National