Bozeman Pass

Bozeman Pass carries I-90 over the gap between the Bridger Range to the north and the Gallatin Range to the south, on the Gallatin and Park county line in southwestern Montana. It sits about 13 miles east of Bozeman and about 15 miles west of Livingston. The summit runs roughly 5,700 ft. Sources put it between about 5,702 ft on the USGS gap reading and about 5,760 ft where I-90 crosses, so treat it as a high climb without trusting any single false-precision number. The National Weather Service labels its forecast point here "Bozeman Pass I-90 MP 321.8," and the grade sits between Bear Canyon Rd at Exit 313 and Jackson Creek Rd at Exit 319.

This is one of the higher I-90 climbs in Montana and a recurring winter chokepoint. It closes again and again through the cold months for blowing snow, whiteout visibility, black ice, and the crashes that follow. The Livingston end is some of the worst high-wind road in the state, and trucks get blown over there. There is no avalanche risk documented for the pass itself, so do not let the elevation fool you into expecting one.

The climb from the Livingston side runs roughly 12 miles by secondary accounts, though MDT does not publish a confirmed maximum highway grade. Gear down for the descent and treat it as a long, sustained grade rather than quoting a hard percent that no DOT source backs. Before you run it, pull the live status from MDT 511 and the NWS point forecast. The pass has no scheduled closures; it shuts without warning, and the only reliable way to know is to check.

• Crosses I-90 between Bozeman and Livingston, at the Gallatin and Park county line, about 13 miles east of Bozeman (Wikipedia, citing USGS GNIS)
• Summit runs roughly 5,700 ft; sources range from 5,702 ft at the USGS gap to about 5,760 ft where I-90 crosses (Wikipedia)
• Separates the Bridger Range to the north from the Gallatin Range to the south (Wikipedia)
• NWS forecast point is labeled Bozeman Pass I-90 MP 321.8, with the grade between Exit 313 and Exit 319 (NWS Great Falls)
• Not the highest pass on I-90 in Montana; Homestake Pass at about 6,375 ft is higher (Wikipedia)
• MDT lists Bozeman Hill among its designated chain-up locations on I-90, alongside Lookout Pass, Homestake Pass, and Cardwell Hill (MDT chains.aspx)
• No scheduled closures and no reliable annual closure count; it shuts event by event during winter storms and high wind

Montana has no fixed chain-control season the way California does. MDT can require chains at any time of year once it declares dangerous conditions in a designated area. Between October 1 and April 30, towing units of 26,001 lbs GVW or greater must carry tire chains or an MDT-approved traction device when running where chains may be required. AutoSock counts as an approved alternative. When chains are declared in effect, every vehicle towing a trailer must put chains on the driver wheels of at least one axle. Four-wheel-drive vehicles are exempt from the carry rule. There is no fixed open or close date for the pass itself. It opens and closes ad hoc as MDT reacts to storms, then reopens once conditions and any wrecks clear. Watch for the posted chain-up and removal signs on Bozeman Hill rather than expecting a published mile marker, since MDT does not publish a specific chain-up pullout location for the grade. (MDT chains.aspx)

Long before the interstate, this gap was a travel route. William Clark's party crossed the pass on July 15, 1806, guided by Sacagawea, while exploring the Yellowstone River on the return leg of the Lewis and Clark Expedition. The pass takes its name from pioneer John Bozeman, who opened the Bozeman Trail in 1863 to run from Fort Laramie, Wyoming, up to the gold camps around Virginia City, Montana.

The railroad came next, and it came underground. The first train ran through the Northern Pacific Railway tunnel under the pass on January 20, 1884, after the east and west headings met the previous December; engineer W. Milnor Roberts had picked the route. A fire blamed on a passing engine broke out inside the tunnel on September 13, 1895, and the damaged bore was out of service for about a year before trains ran again through the rebored tunnel by mid-1896. A newer, shorter tunnel just north of the original opened on July 28, 1945, and the last train ran the 1884 bore that day; the tracks today belong to BNSF Railway. I-90 was built over the pass in the 1960s. (Wikipedia, Bozeman Magazine)