we've been across 20 over to Chadron and up 385. Good two lane road.
have not been north on 83 to I-90, but I wouldn't be afraid to take it.
if you go up 385 and go up through Hot Springs up to Hill City, then 16 on to Deadwood, it will take longer but that is the scenic way to go. Or, you can take 71 when it spurs off.
it will be a faster route for you, but not as scenic.
Holiday Rambler Endeavor LE/ 3126B Cat
( Sometimes ) BMW K75 on Rear Carrier
Jeep Grand Cherokee Toad
M&G aux brake system
854 watts of solar power
Always remember you're unique, just like everyone else.
Dad and I stayed at Valentine and drove 20 to Merriman, north to Martin SD then there's a shortcut through a reservation. Look for a village on the map called Kyle SD. Somewhere between Martin and the back roads into the Badlands it like someone turned on a scenery switch. We were not pulling a camper and had opted to rent one in Montana. All paved roads though.