Christopher -
East of Buffalo, it's a different story.
I am guessing that you plan to visit Bear Lodge Butte (which was & will be the name of Devils Tower).
From there you can work backwards towards Buffalo to plan overnights and services.
It's just shy of 60 miles from Gillette to Bear Lodge, with Moorcroft a nice lunch stop.
So the question becomes, how ya gonna get from Buffalo to GIllette?
Some people ride I-90 because it is much shorter - yuck, bleah, gag.
US 14/16 is 98 very quiet miles with a shoulder much of the way.
Some of the finest High Plains riding there is anywhere.
Which is - for most people - a day and a half of riding.
Options:
A) Spotted Horse; Moorcroft; Bear Lodge.
B) Spotted Horse; Gillette; Bear Lodge.
C) Arvada; Gillette; Bear Lodge
D) Clearmont; Gillette; Bear Lodge
Quite a few people have had negative experiences at Spotted Horse.
They love bikes - i.e. Harleys - but are less keen on pinko-commie cyclists.
They do charge for everything - including water - tap water really isn't drinkable.
There's a funky bar a coupe of miles off route at Arvada.
And you can probably camp by the Powder River.
But Clearmont has been good about letting people camp in the town park.
Clearmont also has a little store with microwave pizza.
(If there's a church pot luck, you can eat until you explode.)
My choice would be Clearmont - leaving early the next morning.
>> Regarding Leiter -
Over the past 15 years or so, Leiter has been closed more than it has been open.
If you planned on staying there and they were closed, you could always go on to Arvada.
But, given how empty this stretch is, I wouldn't count on Leiter.
The most recent owners seem to be doing better, but Covid may have changed that.
The ride from Buffalo to Leiter is along Clear Creek with jagged hills and lush ranchlands.
Ucross is an artists colony - with shows at the Big Red Barn - plus water & restrooms.
Most people don't turn off to Arvada - which is straight out of 1898 -
So, the only place until Gillette Airport is Spotted Horse.
And, really, you should stop for a beverage - at least.
You may get the standard, "You need a motor on that bike" comment, but hey.
https://ridewithgps.com/routes/32686958(Back a few years ago, I rough camped.)
From Spotted Horse to GIllette is damn empty. The shoulder disappears at times.
The traffic picks up as you get closer to GIllette, but it's never much until you hit the 4-lane section.
The Rawhide surface coal mine is now shut down, so you won't see the giant trucks - 25 ft. high.
There's a small campground in town - Green Trees Crazy Woman - that has tenting - the other is RV.
Also, plenty of motels of in all ranges. Most stores are well down Hwy 59 / Douglas Hwy.
Hwy 51 east of Gillette is the old road. Moderate traffic that gets lighter.
The Wyodak surface coal mine is the oldest in the U.S. and still operational.
Moorcroft has motels, private camping, cafes, stock up on groceries.
US 14 towards Bear Lodge is surprisingly hilly. The old store/cafe at Carlile is long closed.
You turn off onto Hwy 24 which takes you to the SD border. Light traffic after the park.
I would get advanced reservations to camp at Bear Lodge N.M.
It's a lovely campground right on a bend in the Belle Fourche River.
The tourist traps on the road leading in charge an arm and a leg. ($55)
https://ridewithgps.com/routes/32686989Hulett, just north, has motels, camping, and cafes.
There's a small, no water NFS campground at the crest of the climb.
Aladdin has a historic and pricey general store/motel.
Pic - Clear Creek near Clearmont