The main populations are found in California, specifically the humid forests of the mountainous areas of Northern California including the Northern Coastal Range of California, the Trinity Alps, the Siskiyou Mountains, and the Sierra Nevada as far south as Fresno.
It is found in the Washington Cascades south of Snoqualmie Pass, Saddle Mountain in the Oregon Coast Range, and the Siskiyou Mountains in south-western Oregon.
This was because the airmail aircraft would have to traverse the 7,000 ft Siskiyou Mountains on the Oregon-California border.
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In 1988, the Supreme Court overturned two lower court rulings that sided with northern California Indians who were trying to prevent a logging road from going through their sacred "high country" in the Siskiyou Mountains, east of Eureka.
The forests in the watershed include a wide variety of vegetation, including Douglas-fir, bigleaf maple, madrone, typical of the Southern Oregon Coast Range, coastal Siskiyou Mountains, and the Redwoods Zone.