From the 7,764 ft. siding at Logan (MP 164.6), where the speed limit is 25 mph, and a branch that is the residual trackage of the former NP line over the now-closed Homestake Pass to Butte, trails in from the west, as the main line bridges to the south side of the Gallatin River and turns curvily east, still single track CTC, with speed limit rising to 60 mph, up the Gallatin River valley, and starts the eastward climb up Bozeman Pass, turning east-southeast past the 3,574 ft. siding at Manhattan (MP 159.3), a bridge back to the north side of the river, Central Park, a detector at MP 154.7, the 7,000 ft. siding at Belgrade (MP 149.9), Story, and the 10,045 ft. siding at Bozeman (MP 140.4), where the speed limit is 40 mph, and the yard is on the southwest side of the tracks, along with wool warehouse, freight and (former) passenger depots.
On the east side of Bozeman, just east of the yard, the line passes an embankment on both sides of the track and the site of a former overbridge on a long departed Milwaukee Road branch line, and turns east-southeast, southeast, east-northeast past Chestnut, northeast past a detector at MP 131.1, where the speed limit has fallen to 30 mph, and just south of due east at the 9,352 ft. siding at West End (MP 128.6), past the crest of the pass at 5,592 ft. elevation, and the 3,015 ft. long Bozeman Tunnel (MP 128.0), and begins the descent of Bozeman Pass, past the 8,685 ft. siding at Muir (MP 127.1), where the speed limit is 35 mph, Hoppers, and the former junction where a spur from Cokedale trailed in on the south side, to the former junction with the erstwhile Gardner Branch from the north entrance to Yellowstone National Park at Gardner, some fifty miles away, which follows the Yellowstone River (which comes north and turns northeast) and east-northeast to the 10,466 ft. siding at Livingston (MP 115.4), where the speed limit is 20 mph, the line crosses the Yellowstone River, the Livingston Rebuild Center is on the north side of the tracks, along with a small yard, and the extensive brick depot is on the south side.
The line, still heading east-northeast, bridges to the south side of the river, following the river valley all the way to Billings and beyond, past a spur at Burkland Lumber Company (MP 112.4), a 5 mile spur at Northern Energy (MP 112.2), a spur at Downer (MP 111.8), where the speed limit has reached the line's maximum 60 mph, a detector at MP 111.1, and Mission (MP 109.7), where an NP branch once headed north, turning just south of due east, past the 10,180 ft. siding at Elton (MP 102.3), north, following the course of the river, northeast past Springdale, and east-northeast, still on the south bank of the river, past the 9,274 ft. siding at Carney (MP 90.9), a detector at MP 86.8, and the 9,306 ft. siding at Big Timber (MP 80.9), and then southeast, with the river, past the 9,322 ft. siding at Greycliff (MP 70.2), and a detector at MP 86.6, east, east-southeast past the 9,093 ft. siding at Quebec (MP 82.0), and east and just south of due east past the 9,436 ft. siding at Reed Point (MP 56.9), and a detector at MP 54.8, where it turns east-southeast.
Between Reed Point and Craver, the line crosses to the south side of the Yellowstone River, turning northeast, east-southeast, south-southeast past the 8,481 ft. siding at Craver (MP 47.6), and a detector at MP 46.6, and just south of due east, all following the north bank of the river, past the 9,231 ft. siding at Columbus (MP 40.3), where the speed limit is 40 mph and there are also storage tracks and lineside industry between railroad and river, a detector at MP 36.1, where the speed limit is back to 60 mph, and the 9,143 ft. siding at Rapids (MP 32.3), turning east-northeast, past Young’s Point, where the Yellowstone River moves away from being right alongside the line, a spur at Park City (MP 22.4), Spurling (MP 17.7), where Two Main Tracks, CTC, start, and Laurel NX (MP 14.9), where the BNSF Casper subdivision (ex-CB&Q) from Bridger Junction, WY (near Orin at the south end of the Powder River coal line) turns away to the south with a wye at the junction, where the speed limit is 40 mph at the junction, and Yard Limits, 10 mph, start for the yard to the east.