Marble Mountain Wilderness, Nature reserve in Klamath National Forest, California, US

Marble Mountain Wilderness is a 241,744-acre (978.30 km2) wilderness area in the Klamath National Forest, Siskiyou County, California, 60 miles southwest of Yreka. Its core is the horseshoe-shaped Salmon Mountains, with Marble Mountain as a north-trending spur and Boulder Peak rising to 8,299 feet (2,530 m). The name comes from light-colored limestone and black metamorphic rock on some peaks, giving a marbled appearance; at least five rock types are found here. The photograph shows a steep, rocky ridge with gray and tan stone, scattered low green shrubs, a dense line of dark green conifers along the crest, and patches of white snow on shaded upper slopes and in gullies.

The area was first protected as a Primitive Area in 1931, then officially designated as wilderness under the 1964 Wilderness Act. This recognition safeguarded the region from development and gave it permanent protected status.

The region features numerous caves with stalactites and flowstone formations, including Bigfoot Cave, which ranks among the deepest in the continental United States.

The wilderness spans elevations from 400 to 8,299 feet, with 32 miles of the Pacific Crest Trail crossing it. Fishing is popular in the 89 lakes and in Wooley Creek and the North Fork Salmon River. Caves are mostly entered by vertical drops and are recommended only for experienced cavers; trailhead signs warn of white-nose syndrome.

The wilderness holds the southernmost stand of Pacific silver fir in the species' range, in the headwaters of the Salmon River. All subalpine fir groves in northwest California, including those around the Sky High Lakes Basin, lie more than 50 miles from the next closest stand, on Mount Ashland in southern Oregon.