Island Park to Keystone: A Realistic Road Trip Guide

The drive from Island Park, ID to Keystone, SD spans 580 miles (933 km) across the northern Great Plains, following US-20 east to I-90. The route passes through Yellowstone's gateway and the Bighorn Mountains, offering a mix of volcanic geology and prairie expanse. One unusual fact: you'll cross the Continental Divide twice—once at Togwotee Pass (elev. 9,658 ft) and again near the Wyoming/South Dakota border—even though the drive generally trends downhill.

The journey takes roughly 9.5 hours of pure driving time, but plan for 2–3 days to appreciate the sights. The fastest path via I-90 is 470 miles, but the scenic detour through the Bighorn National Forest adds 110 miles and a stunning mountain pass. Most travelers prefer the longer route for its varied landscapes.

Gas stations are sparse along US-20 west of Buffalo, Wyoming, so fill up in Cody, Thermopolis, or Buffalo. Expect fuel prices at least $0.30/gallon higher in small towns than in larger cities. The route is essentially a mix of two-lane highways and interstate, with the Bighorn Scenic Byway (US-14) offering standard pavement but occasional narrow shoulders.

Weather can be extreme: summer highs reach 90°F, but mountain passes can receive snow even in June. The route crosses the arid Bighorn Basin, where rainfall averages under 10 inches annually. For real-time road conditions, call 511 in Wyoming or South Dakota.

• Best stops Island Park, ID to Keystone, SD include Buffalo Bill Center of the West in Cody (admission $21).
• How long to drive Island Park, ID to Keystone, SD: about 9.5 hours without stops.
• Is it worth driving Island Park, ID to Keystone, SD? Yes, for the geological and historical variety.
• Things to do between Island Park, ID and Keystone, SD range from dinosaur fossils to mountain driving.

Leaving Island Park, you skirt the edge of Yellowstone National Park, visible from US-20 near West Yellowstone. The region is part of the Yellowstone Caldera, one of the largest active volcanic systems on Earth. As you head east, the landscape shifts to the high deserts of the Bighorn Basin, home to the Thermopolis Hot Springs, the largest mineral hot spring in the world.

In South Dakota, you'll encounter the Black Hills, a granite uplift that hosts Mount Rushmore and the Crazy Horse Memorial. The area is also home to Wind Cave National Park, a maze of passages that is one of the longest caves on the planet. These parks are centered around the town of Custer, which serves as a gateway for many travelers.

Local commerce along the route is dominated by small-town diners and roadside attractions. In Buffalo, Wyoming, the Occidental Hotel has hosted Theodore Roosevelt and Buffalo Bill. In Keystone, you can find traditional jackalope souvenirs and Black Hills gold jewelry, a local specialty.

Road quality on I-90 is excellent, but the two-lane sections can be tricky at night due to deer and elk. In Wyoming, livestock grazing areas are unfenced, so watch for cattle on the road. Always carry water and a spare tire, as cell service is spotty west of Buffalo.

For families, the Buffalo Bill Center of the West is a hands-on museum with a natural history wing. Kids also enjoy the Mammoth Site in Hot Springs, SD, where they can view fossilized mammoths in an active dig. These stops are both family-friendly and educational.

If you travel with pets, many hotels along the route are pet-friendly, but national parks have strict pet rules—pets are only allowed on paved paths and must be leashed. To prevent fatigue, plan a break every two hours. The rest areas near Gillette, Wyoming, offer scenic picnic spots and bathrooms.

Hidden off-route gems include the Medicine Lodge Archaeological Site, with ancient rock art, and the Devil's Tower, a volcanic intrusion that rises 1,267 feet. For a break from driving, consider the Wind River Canyon, a scenic gorge just south of Thermopolis. To plan your stops more efficiently, use a tool like how to find the best stops and hidden gems between cities.