This tunnel sees very little light in winter. Th west portal is so shaded by the canyon, that the portal will have about a 30 minute window where it's lit. Otherwise, it's in deep shadow. The east portal is shaded by trees, and may not see any direct sunlight in winter.
I was correct earlier, when I said "Brrrr." I've worked in places like this. I understand. Really blows your mind, when it's June, and you're bundled up like it's still February. Boxcab E50