Ketchum to Thermopolis: Road Trip Guide for Adventurers

Did you know that the route from Ketchum, ID (elevation 5,900 ft) to Thermopolis, WY drops nearly 2,000 feet in elevation, crossing the Continental Divide twice? This 330-mile drive along US-20, US-26, and WY-120 passes through diverse ecosystems, from alpine meadows to high desert badlands.

US-20 from Ketchum to Idaho Falls is a well-maintained two-lane highway with sections of passing lanes. The speed limit is 65–70 mph. From Idaho Falls to Shoshoni, US-26 runs alongside the Snake River before cutting through remote Wyoming ranchland. The final leg on WY-120 features long straightaways with occasional dips.

• Fuel stops every 30–50 miles: key stations in Carey, Arco, Mud Lake, Rigby, St. Anthony, Ashton, Dubois, Shoshoni, and Thermopolis.
• Last reliable fuel before Thermopolis is in Shoshoni, 45 miles east.
• Cell service: limited west of Rigby; AT&T has sporadic coverage; Verizon better in Idaho, weak in central Wyoming.
• Towing services available in Idaho Falls, Dubois, and Thermopolis (24/7).

Road quality is good except for sections between Mud Lake and St. Anthony where frost heaves create bumps. Wildlife (deer, antelope, moose) is common at dawn/dusk—use high beams when safe. Speed enforcement is strict in small towns (e.g., Arco speed trap at 25 mph zone).

• Family & Child Suitability: Fun stops include the Idaho Potato Museum (Blackfoot, 10 min detour) and the Wind River Canyon dinosaur tracks.
• Pet-Friendly: Most rest areas allow leashed pets; Craters of the Moon has a pet loop but no pets on trails.
• Fatigue Management: Rest areas at mile markers 100 (near Carey) and 210 (near Dubois). Shoshoni has a 24-hour diner for coffee breaks.
• Hidden Off-Route Spot: Goldstone Hot Springs (10 miles south of Dubois) is a primitive natural soak—look for the parking pullout.

The route transitions from the Sawtooth Mountains to the Snake River Plain, then into the Absaroka Range. Notable geological features include Craters of the Moon National Monument (lava fields) and the Wind River Canyon (11-mile scenic gorge).

• Natural Landscapes: Craters of the Moon lava tubes, Hell’s Half Acre (Spencer, WY), and the Bighorn Basin rock formations.
• UNESCO World Heritage Sites: None directly on route, but Yellowstone (south entrance 2 hours north of Dubois) is a UNESCO site.
• Local Commerce: Ketchum's upscale boutiques contrast with Dubois' rustic trading posts selling bison leather and Rocky Mountain souvenirs.
• Climatic Conditions: Expect afternoon thunderstorms in July; winter temps below -10°F in Wyoming sections. Dress in layers.