About Our Watersheds


Upper Sacramento

The Upper Sacramento River watershed is approximately 600 square miles in size with flows originating on the western slopes of Mount Shasta and eastern side of the Eddy and Trinity Mountains. The Upper Sacramento River has significant flows year-round due to abundant spring water fed by Mount Shasta’s glaciers. Many small natural alpine lakes are scattered along the crest of the Upper Sacramento and Trinity River watershed divide, including Castle Lake, Grey Rock Lake, Cliff Lake, Toad Lake and others. The most significant reservoir in this watershed is Lake Siskiyou, which lies behind Box Canyon Dam and represents the only impoundment on the Upper Sacramento River between the headwaters and Shasta Lake.

The Upper Sacramento includes the majority of the Region’s population including the cities of Dunsmuir and Mt. Shasta, as well as a number of small communities along the river south of Dunsmuir including Cragview, Castella, Sweetbrier, Pollard Flat, and Lakehead.


The McCloud River Watershed covers approximately 800 square miles draining the south and east sides of Mount Shasta as well as the range to the south of the volcano. Like the Upper Sacramento River, the McCloud has steady year-round flows due to numerous productive springs feeding into the system, most notably McCloud Big Springs, with an average discharge of 600 cubic feet per second. The McCloud is world-renowned as a fly fishing destination with abundant rainbow trout. The watershed also supports populations of endemic McCloud redband trout, which is found in isolated populations in a few tributaries in the upper watershed.

As part of the PG&E McCloud-Pit Hydropower Project, the McCloud River is partially diverted at the McCloud Dam into the Pit River via the McCloud-Iron Canyon diversion tunnel. As much as 90 percent of water flowing in the Upper McCloud River has been diverted to the Lower Pit River watershed in this manner. The McCloud reservoir is the most significant surface water body in the McCloud watershed.

Human populations in this watershed are concentrated in the town of McCloud. Prior to European settlement, the McCloud watershed was home to significant tribal populations, and many cultural sites used by local tribes to this day are located within the watershed. 


Lower Pit

For the purposes of the IRWM Plan, the Lower Pit watershed extends from directly below Lake Britton to the edge of Shasta Lake, covering approximately 700 square miles. (The watershed above Lake Britton is included in the adjacent Upper Pit IRWM Planning region.) To the west and north, this area in bordered by the McCloud River watershed described above. Major boundary features to the east include the dam at Lake Britton, Hatchet Mountain and Hatchet Mountain Pass. For the purposes of the IRWM Plan the “Lower Pit River” area also includes the watershed of Squaw Creek which flows directly into Lake Shasta between the outlet of the Pit River and the McCloud River arm of the lake.

As noted in the description of the McCloud River watershed, a considerable amount of water is diverted from the McCloud River to the Pit River via the McCloud-Iron Canyon diversion tunnel. In addition to Iron Canyon Reservoir PG&E operates a series of dams on the Lower Pit River forming several additional reservoirs along the river. Human populations in this watershed reside primarily on Pit River Tribe reservation lands clustered around the community of Big Bend on the Pit River.

Medicine Lake Highlands

The Medicine Lake Highlands, which is the northeastern-most area of the Upper Sac IRWM region, is an area comprised of a massive shield volcano. The broad, gently sloping mass of this volcanic feature covers approximately 200 square miles. While not recognized as a typical watershed due to the lack of streams, much of the area of the Medicine Lake Highlands is considered to be a significant recharge area, via subsurface flows as opposed to surface drainage, to springs that feed Fall River. Fall River, which is outside this IRWM region, is a tributary to the Upper Pit River. The area of the Medicine Lake Highlands that is in the Upper Sac IRWM region includes the caldera in which Medicine Lake itself is located, and the south and southwesterly slopes of the highlands to where it converges with the McCloud River watershed. Medicine Lake, from which this area derives its name, lies in a caldera near the top of the highlands at an elevation of approximately 6,680 feet.

The Medicine Lake Highlands is predominantly comprised of public land managed by the U.S. Forest Service, and there is no resident human population. The area is of cultural significance to many local tribal groups.