This species occurs from southern British Columbia in Canada through the USA to Baja California, Mexico, then east to Montana, Idaho, and Nevada. It also occurs on the Channel Islands off southern California (Behler and King 1979). Desert populations in southern California were probably introduced. It is introduced on Queen Charlotte Islands, British Columbia (Reimchen 1990), Canada. It was recently found on Revillagigedo Island in Alexander Archipelago, Alaska, where it is probably breeding and was possibly introduced (Waters 1992). It occurs from sea level to over 3,000m asl.