Just outside the west entrance to Yellowstone (I think it's only 3-4 miles away from the entrance) is a good backup campground in case you can’t get a campsite in the park (a common problem in the summer season). This busy first come, first served campground is run by the Forest Service, so you are really relying on solid campground hosts if you need help (and they were great!). There are 70+ sites with use very mixed, meaning you could have a tent on one side and an RV on the other, however the electric sites are all grouped together along the road and the non-electric sites are along the river. Most of the sites had at least a few trees, some had many, so there will be likely be a spot to hang your hammock. The tent pads were gravel, so they drained well, but not the best for comfort or east of staking. Toilets were clean and there was a nice fishing dock on the river. If you need a shower there is a laundromat on the north edge of West Yellowstone as you come into town that has pay showers.