Shasta-Trinity National Forest, National Forest in Northern California, United States.

Shasta-Trinity National Forest covers 3,454 square miles (8,945.5 km²) across six northern California counties, making it the state's largest national forest. It includes five wilderness areas, hundreds of mountain lakes, and 6,278 miles of streams and rivers. Shasta Lake, California's largest man-made lake, and Mount Shasta, at 14,179 feet, are major features.

The United States Forest Service created Shasta-Trinity National Forest in 1954 by combining several previously separate forest areas into one managed region. This merger brought multiple forest protection efforts under unified management.

The forest lies at the junction of the Eastern Klamath Mountains and the Southern Cascades, a boundary noted by Miles and Goudy in 1997. C. Hart Merriam's 1899 biological survey of Mount Shasta recorded the vegetation zones and wildlife that later researchers still consult. The main stem of the Trinity River is a designated National Wild and Scenic River.

The forest spans 3,454 square miles, with 6,278 miles of streams and rivers and five designated wilderness areas. Access is via Interstate 5 and California State Route 299; the Shasta and Trinity units are managed jointly from Redding. Check road and fire conditions before setting out, as many backroads are unpaved.

Mount Shasta rises about 14,179 feet and dominates the landscape as one of the tallest peaks visible throughout the forest region. This snow-capped volcanic mountain can be seen from many locations within the forest and serves as a landmark for visitors.