Lost Lake Guard Station is a historic Forest Service building in the Okanogan–Wenatchee National Forest near Tonasket, Washington. Built in 1940 by the Civilian Conservation Corps and designed by the U.S. Department of Agriculture Forest Service Architecture Group for the Pacific Northwest, it reflects the Rustic style. The building is significant as an outstanding example of the Forest Service’s regional rustic design tradition, which used early twentieth-century American architecture to express the agency’s identity, purposes, and ideals. Its importance was formally recognized when it was added to the National Register of Historic Places on April 11, 1986.