Castle Lake is a glacial lake (cirque lake or tarn) located in the Trinity Mountains, in Siskiyou County of northern California. It is west of Mount Shasta City and Mount Shasta peak.
The outlet of the lake drains into Castle Lake Creek, and then into Lake Siskiyou reservoir, part of the headwaters of the Sacramento River. Nearly all of the lake's are within the Shasta-Trinity National Forest. Trails lead from Castle Lake into the adjacent Castle Crags Wilderness area, and on to Castle Crags State Park, including trails to Little Castle Lake and Heart Lake. Fishing, camping, and hiking are also available at or near the lake.
Natural history
Castle Lake and the surrounding area contain a wide variety of animals and plants including trout, bears, deer, otters, frogs, and osprey. The area is also well-known for early summer displays of flowers, including red Columbine (Aquilegia truncata), fawn lily (Erythronium sp.), and Shasta pentstemon (Pentstemon laetus).
Castle Lake is home as well to the Castle Lake Limnological Research Station affiliated with the University of California at Davis (UC Davis), which uses the site for study and to teach limnology courses (in conjunction with the University of Nevada, Reno).
Recreation
The lake is usually reached by driving along an approximately road from Lake Siskiyou. About from the lake, along this road, are Ney Springs and Faery Falls. Ney Springs is the site of the historic Ney Springs Resort, a late 19th-century resort based on the mineral springs there; this resort was one of a number of such popular resorts in Siskiyou County, including Upper Soda Springs, and Shasta Springs. A short hiking trail leads to nearby Faery Falls, where Ney Springs Creek falls nearly down a granite cliff face, forming a clear pool at the bottom.
About one-quarter mile (400 m) north of Castle Lake is a campground with 6 first-come, first-served campsites. At the lake itself, fishing and picnicking, as well as viewing the local plant life, wildlife and scenery, are common activities. The lake waters can be cool, so swimming is generally limited to summer months. Kayaking, rowboating and rafting are available on the lake. In the winter, in addition to cross-country skiing and snow-shoeing along the trails in the area, the lake will ice over and ice fishing is a common activity.
From the parking area at the lake, a half-mile (1 km) trail winds along the northern and western shore of the lake, ending at the granite face of the headwall, which forms the southern shore. Along the way, hikers will pass the Castle Lake Limnological Research Station.
Following the eastern shore, the Little Castle Lake Trail leaves the parking area, and then climbs the adjoining ridge; about along this trail is Little Castle Lake, a small glacial tarn reached by passing through meadows of wild flowers in the early summer. Little Castle Lake is within the Castle Crags Wilderness Area. Heart Lake, another small tarn, located above the headwall of Castle Lake, may also be reached via an informal cut-off from the Little Castle Lake Trail.
At this point, the well-known Pacific Crest National Scenic Trail is one-half mile (1 km) away, just over the Trinity Divide. The Pacific Crest National Scenic Trail stretches from Mexico to Canada, following the highest portion of the Sierra Nevada, Klamath Mountains, and Cascade Range and paralleling the Pacific Ocean by .
The Little Castle Lake Trail continues on to Mt. Bradley, a locally prominent mountain with views of Mount Shasta, overlooking Dunsmuir, California and the canyon of the Upper Sacramento River. Along the way, the trail joins with a network of connections leading into Castle Crags State Park.
Formation
The lake's origins date to the Pleistocene Era (more than 10,000 years ago) when a glacier carved a basin in the location of the current lake. During that era, much of North America was glaciated. Castle Lake is a typical glacier cirque lake (or tarn), reaching depths of up to near the southern, granitic part of the lakeshore (the cirque face). There is a terminal moraine of boulders and gravel forming a natural dam opposite the cirque face along the northeastern shore of the lake, where there is an outlet, and the lake is deep.