John, I did a Google search for Sumpter Valley Dredge, and got too many sites to list (1200 to be exact). I see the dredge everytime I'm at Sumpter (about twice a month this past season), but haven't toured it for some time now. It has been closed most of this past tourist season for repairs, but should be opened next season.
It is facinating to walk through. It is a self guided free tour, and the park ranger is often available to answer questions. Only the first floor has been open for safety reasons.
www.friendsofthedredge.com/
www.historicsumpter.com/sumpter-oregon-dredge-park.html
www.oregonstateparks.org/park_239.php
www.oregonstateparkstrust.org/OurWork/EasternOR/sumptervalley