The Klamath Mountains, sometimes called the Salmon Mountains, are a rugged lightly populated mountain range in northwest California and southwest Oregon in the United States. The highest peaks are Mount Eddy (9025 ft / 2750 m) in Siskiyou County, California, Thompson Peak (9002 ft / 2744 m) in Trinity County, California, and Mount Ashland (7,533 ft / 2296 m) in Jackson County, Oregon. They have a varied geology, with substantial areas of serpentine and marble, and a climate characterised by a moderately cold winters with very heavy snowfall, and warm very dry summers with limited rainfall. As a consequence of the geology, they have a unique flora, known as the Klamath-Siskiyou forests, which includes several endemic or near-endemic trees, such as Port Orford cedar (Chamaecyparis lawsoniana), Foxtail pine (Pinus balfouriana spp, balfourinana), Brewer spruce (Picea breweriana) and Kalmiopsis (Kalmiopsis leachiana), forming one of the largest collections of different conifers in the world. The northernmost range of the Klamath Mountains are known as the Siskiyou Mountains. The area is also home to a diverse array of wild fish and animal species, including nine species of salmonid, and bears, large cats, and eagles. Physiographically, they are a section of the larger Pacific Border province, which in turn are part of the larger Pacific Mountain System physiographic division.
The many mountains, streams and rivers form a major spawning ground for several species of trout and salmon, yet recently, in the last 50 years, some of the fish stocks have fallen drastically, particularly salmon stocks. The ecoregion's rivers and streams are home to nine species of native salmonids. The depletions occur mainly because the creation of dams and excessive clear cut logging on the steep rugged slopes of the area both contribute to large amounts of silt in the stream beds, which in turn interferes with the salmon spawning, as they need exposed gravel beds in which to lay their eggs. Other notable fish species, besides king salmon and silver salmon, include steelhead, brown trout, rainbow trout, kokanee salmon, eastern brook trout, crappie, bluegill, catfish, large and smallmouth bass.
Conifer species include Coast Douglas-fir (Pseudotsuga menziesii subsp. menziesii), Lawson's Cypress (also known as Port Orford Cedar, Chamaecyparis lawsoniana), Ponderosa Pine (Pinus ponderosa), Sugar Pine (Pinus lambertiana), Mountain Hemlock (Tsuga mertensiana), White Fir (Abies concolor subsp. lowiana), Red Fir (A. magnifica subsp. shastensis), Weeping Spruce (Picea breweriana), Coast Redwood (Sequoia sempervirens), Western Red Cedar (Thuja Plicata), and Pacific Yew (Taxus brevifolia).
Typical species of the Trinity Alps region include Douglas fir, ponderosa pine, red fir, white fir, black oak, canyon live oak, Pacific madrone, bigleaf maple, California buckeye, incense cedar, and Jeffrey pine. California's northernmost stand of Digger Pine is found here along the South Fork of the Salmon River.