This belongs near the top of rides you must experience in Oregon. The trail apparently has three sections - the lowest goes through old growth forest and follows the stream part of the way. Though I didn't get to try on this trip., the middle section passes waterfalls and the top section runs through lava fields.
The temps were 105 degrees when I tried, so I stuck to the lower trails, which are shaded. The full trip is roughly 26 miles one way - next time I will likely do a shuttle (there are still plenty of opportunities to get uphill exercise even on the 'downhill'). I'd consider an ending point around Belknap Resort - the section from Belknap west to the trails end is a bit of an up-and-down slog, maybe not what you want at the end of your trip. But still fun if you have the energy.
And it is ALL single track.