My guess is that the dotted purple line on the map you describe almost certainly depicts a dozer cut fireline from the 1977 firefighting effort. The way it sticks to the ridgeline instead of following a countour makes it seem much more like a fireline than a trail. At least until it gets down into teh SEQ of section 11, then 12 and 13 near Piney Creek camp, where it looks much more like a travel route.
It still shows up pretty well on the Terraserver, which is based on 1994 photos. Check out the link below.
