This is a really fantastic and recently-reopened horse camp in Santiam State Forest. We just stayed for a night on 7/30 and found it to be really nicely set up in many ways. There's plenty of privacy between sites, well-established trails between and around the campground, and very easy access to tons of different trails. The maps they provide are easy to read and the signage is clear. The corrals are made with beefy 10-inch round logs with just enough space for our horses to comfortably move around.
This will be on our short list of places to horse camp. The only minor drawback is that the haul-in route is over gravel forest road, which can be steep and skinny in places. I'd recommend 4X4 trucks to be used for hauling more than 2 horses in.