A night on Rock Creek puts you at the bottom of the Beartooth Highway switchbacks, the creek still loud in the canyon and the Beartooth Range standing over camp before you climb toward Cooke City. US-212 leaves Red Lodge and climbs the canyon wall, switchbacks stacking above the water, past grizzly-country signs at the trailheads. The far side drops to Cooke City and Silver Gate, Yellowstone's northeast entrance, and you only get this crossing in summer while the pass is clear.
Parkside is the first-night campground, the largest of the three national forest camps on Rock Creek and the one at the base of those switchbacks, a little over an hour from Billings on US-212. From Billings it is the same-day drive out, then the climb in the morning. If Parkside is full, Limber Pine and Greenough Lake are the overflow, a mile apart on the same road.
Greenough Lake caps a van at 35 feet and Limber Pine takes vehicles up to 55 feet. If you need more sleeping space or a longer rig than those spurs allow, look at Montana RV rentals.
Cooke City is at the far end of that descent, Silver Gate and the northeast entrance just beyond. You can spend a day through the gate and still sleep back on Rock Creek. Soda Butte and Colter are just east of Cooke City if you want the night next to the park.
Bighorn Canyon
South of Billings the Bighorn River becomes a reservoir between cliff walls, sagebrush and juniper on the benches above the water. Afterbay is the Montana camp near Fort Smith, open all year with electric and water hookups and no reservations.
Horseshoe Bend is across the Wyoming line near Lovell, a longer shore under those walls, with a 35-foot limit. Hookup water there runs Memorial Day through Labor Day, and electricity stays on year-round. Wild horses still run the Pryor Mountains above the canyon.
Pompeys Pillar is a 120-foot sandstone block off I-90 from Billings, with a boardwalk of switchbacks up to the rock face where William Clark cut his name in 1806. Little Bighorn Battlefield is white markers on Last Stand Hill, a grass slope after the drive in.
Pictograph Cave, on the edge of Billings, is a short loop past three caves with paintings more than 2,000 years old, and it does not allow camping. Lake Elmo is the in-town reservoir, a walking path around the water, also day-use only.
Yellowstone's north entrance at Gardiner is a Bozeman trip. Once you are through the gate, the loop is on Yellowstone. The plains east of Billings are on the Montana hub.