Shellrock Mountain’s BPA -service trail off-trail hiking loop, following the 1872 Wagon Road to finish the loop. Columbia Gorge access near Wyeth exit 51. Exact hiking/scrambling details in Curious Gorge 4.
The photo below is circa 1952 when current I-84 was under construction at the base of Shellrock Mtn. On the talus slope of Shellrock you can see the powerline service trail which had been constructed circa 1938 along with the original BPA powerlines through the Columbia Gorge.
Below are some photos from the entire Shellrock Mtn off-trail loop adventure, including the BPA powerline service trail: