Wow, those are well preserved. The results are all the more brilliant given the undoubtedly great bulk of equipment O'Sullivan was hauling around (by the mule wagon shown in Photo 12) and the presumably extremely slow "film" he was using--wet collodion plates. I'm thinking he was not fortunate enough to have a constant 20 deg C work environment, either.
About 15 years ago I made a photo (albeit not with a rangefinder) quite similar to Photo 19, the confluence of the Green and the Yampa, now in Dinosaur National Monument. I might even be able to find it here somewhere and scan it ... Anyway, fabulous country out there.