The Ishi Wilderness is a 41,339 acre (167 km sq) wilderness area located on the Lassen National Forest in the Shasta Cascade foothills of northern California, United States. The Ishi Wilderness is located approximately twenty miles east of Red Bluff, California. The wilderness was created when the US Congress passed the California Wilderness Act of 1984. The land is etched by wind and water, and dotted with basalt outcroppings, caves, and unusual pillar lava formations. The land is a series of east-west running ridges framed by rugged river canyons, with the highest ridges attaining elevations of 4,000 feet (1,200 m). Deer Creek and Mill Creek are the principal drainages and flow into the Sacramento River.
The Ishi Wilderness is the only protected area in California that preserves a significant portion of the Sierra/Cascade foothill region of the southernmost Cascade Ranges.
The largest migratory deer herd in California, the Tehama deer herd, winters in this wilderness area. Wild hogs, mountain lions, black bears, coyotes, bobcats and rabbits also live here. A State Game Refuge, where hunting is not permitted, occupies most of the Ishi Wilderness.