I just toured the Rock Cr. Plant (just over the mountains from Sumpter), decommisioned in 1995, and recently purchased by a couple very cool guys who own Eastern Oregon Light & Power., Inc. They are trying to re-license it and put the power back on the grid. It was built around 1904 and changed very little since then. Even the very cool marble switchboard and gorgeous gauges are intact. The safety covers on the flyball govenor and sides of the generator are new. It has 2 Pelton wheels.
They plan to keep everything historic, although they will have to use some modern equipment. All will be left, but the modern stuff will be in another room.