The "Alice Ross" tour boat on Diablo Lake, on the Skagit Hydroelectric Project, above the town of Diablo, Washington.
Although the caption of the postcard mentions Mount Baker and its reflection in Diablo Lake, in fact Mount Baker is not visible at any time from any part of Diablo Lake.
The dam was completed in 1930 so the estimated vintage of this hand-colored image is 1930s.