Thermopolis to Spearfish: Wyoming's Wild Road Trip

The drive from Thermopolis, WY to Spearfish, SD covers roughly 220 miles via US-20 and I-90, a journey that traces the ancient shoreline of the Western Interior Seaway. This is a land where 200-million-year-old dinosaur bones dot the hills and the landscape shifts from desert badlands to pine-clad mountains.

The route's centerpiece is the Bighorn Basin, a geological bowl cradled by the Owl Creek and Bighorn mountains. As you crest the Powder River Pass at 9,666 feet, the air thins and the views stretch for 100 miles—a reminder of the raw power that shaped this terrain.

The Bighorn Basin is a fossil hunter's paradise; the Thermopolis area has yielded everything from dinosaur eggs to ancient marine reptiles. The Wyoming Dinosaur Center in Thermopolis displays over 30 mounted skeletons, and public digs are available seasonally.

Further east, the town of Tensleep owes its name to the local Sioux word for 'stiff leg,' a nod to the steep trails that once challenged horse travelers. Today, its general store sells handcrafted leather goods and local honey.

As you descend into Spearfish, the landscape transforms into the Black Hills, a region sacred to the Lakota. The Spearfish Canyon area is part of the proposed 'Black Hills National Forest' but holds no UNESCO World Heritage status—the only such site nearby is the Mount Rushmore National Memorial, 45 minutes south.

Local commerce thrives on ranching and tourism; expect to find artisan roasters and bison jerky shops along the way.

For more on discovering unique stops, check out this guide: how to find the best stops and hidden gems between cities.

Driving weather varies drastically—summer storms can bring hail on the pass, while winter snows often close US-14 between November and April. Always check conditions at the Wyoming Road Report before departing.

For families, the Thermopolis Hot Springs State Park offers a free state bathhouse with 100-degree mineral waters, perfect for a pre-drive soak. Kids will also love the walking trail along the Bighorn River, where pronghorn antelope roam.

Pet-friendly stops are plentiful: the Buffalo (WY) KOA has a dog park, and Spearfish's Community Caves (undeveloped) allow leashed dogs on the rim trail.

To combat fatigue, plan to stop at rest areas near Shell Falls (mile 75) and Lake DeSmet (mile 130), both scenic and quiet. Rotate drivers every two hours, and carry a paper map in case of GPS loss.

Hidden gems just off the route include the Hull's Gulch hiking trail near Ten Sleep, and the historic Hotel Thermopolis, which claims to be the oldest operating hotel in Wyoming (founded 1902).

Begin on US-20 east out of Thermopolis, following the Bighorn River before climbing into the Bighorn National Forest. Near Greybull, you'll pick up US-14 eastward, crossing the Bighorn Mountains via the scenic Shell Canyon.

• Fuel stops: Greybull (mile 60), Basin (mile 35), and Buffalo (mile 150) are reliable; fill up before heading over the pass.
• Cell service: Sparse on the pass; download offline maps.
• Road quality: Well-maintained, but watch for wildlife on the shoulders.

The route joins I-90 at Buffalo, heading east to Spearfish. South Dakota's Spearfish Canyon Scenic Byway (US-14A) is an optional 19-mile detour with waterfalls and limestone cliffs.

For those asking, is it worth driving Thermopolis, WY to Spearfish, SD—the answer is a resounding yes, especially with the natural and cultural gems along the way.