Siskiyou Wilderness, Federal wilderness area in northern California, United States.

Siskiyou Wilderness covers 182,802 acres across the Six Rivers, Klamath, and Rogue River-Siskiyou National Forests. Elevations run from 770 feet to 7,309 feet at Preston Peak. The South Fork of the Smith River forms much of the western boundary, where an ophiolite exposure is visible.

The California Wilderness Act of 1984 first protected 153,000 acres of the Siskiyou Mountains, managed by the U.S. Forest Service across the Six Rivers, Klamath and Rogue River-Siskiyou National Forests. The Northern California Wild Heritage Act of 2006 added 30,122 acres, bringing the area to 182,802 acres.

The name Siskiyou has a debated origin: it may come from an Indigenous language meaning "short-tailed horse," or from the French "Six Cailloux" (six stones), given by French-Canadian trappers to a ford in the 19th century. The wilderness also holds one of the world's largest concentrations of lily species.

The terrain here is rough and demanding, requiring good physical preparation especially due to elevation changes. Summer through early autumn offers the best conditions, when trails are snow-free and weather is more stable.

Around the South Fork of the Smith River, which forms much of the western boundary, the rock shows one of the world's best exposures of ophiolite, a slice of ancient ocean floor. The wilderness also holds one of the world's largest concentrations of lily species and up to 20 conifer species.