OSB

Old Stone Building, at the confluence of San Juan Creek and an unnamed side drainage, Toiyabe Range, Nevada. The ruin isn't even marked on the USGS 7.5' topo map. I suspect it's mining related--there are some old mines and prospects a bit farther up San Juan Creek, now considered part of the Washington District, but there was also some pre-1848 activitiy (i.e., Mexican or Spanish), and this may date from then.