The other week there was a post Go Exploring and that is what I recently did. One of the sites visited played a major role in Lassen County development, though there is no historical marker and in addition no reference on maps. The initial concept was in 1875, construction began in 1881 and the site was not abandoned until 1917.
I think this is the original tunnel in Willow Creek.
Must be the canal from Eagle Lake
Eagle Lake Tunnel #2 out of three
Tunnel construction on the Northeast side of Eagle Lake? (not the Bly ditch)
Looks like some where on the ditch from Eagle Lake and the tunnel to Willow Creek Valley. Just a guess..