The Ishi Wilderness is a 41,339 acre (167 km2) 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.