Underhill is a strange Forest Service campground. It doesn't have an official sign, nor does it appear on the website’s list of campgrounds. And yet here it is: a scruffy, seemingly much-ignored patch right off the Dufur Valley Road. When I visited, the vault toilet's lock was broken and the steel door had some sizable bullet holes in it. It was, however, a clean facility, and someone had even put a lined trashcan inside. The two (or is it three?) campsites are austere — not many trees, no nearby body of water, no privacy and no particularly compelling views— but there is that building, which has a fairly decent roof over it, a massive picnic table inside, and a seriously burned-out wood stove that no one should even think of using.
I'd pitch a tent here if Eightmile, Lower Eightmile, Pebble Ford, Knebal Springs and Fifteenmile were all full, and I didn't bring the necessary for dispersed camping. Call it a fallback-fallback-fallback option. On the upside, it's free!