This is the Electra Power House, on the Mokelumne River near Jackson, California. This building, owned by Pacific Gas & Electric Co., was built in 1948 and replaced the original Electra Power House, built in 1901. It was famous because the power line from it to the S.F. Bay area, used the unique Fred M. Locke combination glass and porcelain multipart insulators. I saw none of those laying around when I was there.