Jeffro,
I hear you, on the 'sketchy'; no landmarks on the Bishop story and few on the Frenchmen. I'm thinking cabin; two big downed trees over a rock back wall. Trees are rotted away but rock upthrusts do not rot. Wind that would drop two big trees had to come from the West. Remember the big wind that layed all the trees down at Eagle Creek, up 58, a few years back. The tops all laying to the East.
I'm also thinking 'placer', which means on-site year-round(Summer-late Summer) water to work it. Bishop's trips were not long enough to have dug it out of hardrock. Besides, where I'm looking is directly between, N. to S., two exposures of the Blue Lead, that I have found. Both up high, near Albany on the North and near Roseburg on the South.
Bud