The diversity of freshwater mussels in Colorado is low compared to other regions of the U.S.A., with only three extant species (down from seven a century ago). The western ridged mussel (Gonidea angulata) occurs in Pacific Coast drainages from British Columbia to California and eastward to Idaho and Nevada. It has been reported from Colorado based on a single museum specimen from Clear Lake, representing a significant range expansion for this species. During extensive recent surveys, I was unable to pinpoint this locality and regarded it as questionable. Examination of the specimen and locality data indicated this specimen was collected from Clear Lake, Lake County, California.