Just passed the Eagle Creek Campground on Jardine Road. Take a left and drive in 3 miles on National Forest Road to areas where camping is allowed. There are mile marker signs. These are mostly little pull offs along the side of the road with great views into Yellowstone/Mammoth Hot Springs. There are more than a dozen good spots, but it also seems popular as I saw at least 10 occupied sites on a Monday evening. No cellphone service. No amenities, just the view and personal space. My Honda fit made it up the road no problem.