Gilmore and Pittsburgh Railroad - Route

Route

The route of the G&P was remote, thinly populated, and often rugged. The line began at the small hamlet of Armstead, Montana, a station stop on the Oregon Short Line Railroad's route between Idaho Falls, Idaho and Butte, Montana. (The Oregon Short Line was a long-time subsidiary of the Union Pacific Railroad, and was later absorbed into that system.) Armstead was in a high valley of the Beaverhead River, in a region known for livestock grazing. The G&P maintained a small yard there, and it was the site of the railroad's corporate office.

From Armsted, the railway headed almost due west, traversing a thinly-populated ranching region known as Horse Prairie. The area provided additional livestock traffic for the railroad, and there were mines in the nearby mountains. Substantial areas of cut and fill were required as the railroad ascended the prairie. The railroad curved southward near the western end of Horse Prairie. and began its ascent of Bannock Pass.

Bannock Pass, on the Idaho-Montana border and the Continental Divide, was by far the most substantial obstacle encountered by the G&P. The pass itself is at an elevation of 7,681 feet (2,341 m), some 1,800 feet (550 m) higher than the center of Horse Prairie. Temporary trackage was built over the top of the pass during the G&P's construction, but a tunnel beneath the pass was clearly needed for the railway's permanent use. Since a tunnel to completely bypass the heavy grades of the pass was prohibitively expensive, the railroad compromised by boring a shorter, 600-foot (180 m) tunnel at the 7,575-foot (2,309 m) elevation. To bring the tracks to the elevation of the tunnel, the railroad line included a switchback on each side of the summit; trains ascending the pass would pull into the first switchback, run backwards through the summit tunnel, and then reverse direction again at the switchback on the opposite side.

Descending Bannock Pass, the railroad followed a narrow canyon into Idaho's Lemhi Valley and the small agricultural community of Leadore, some 55 miles (89 km) from Armstead. The G&P's repair shops were at Leadore, and it also marked a junction point for the railway. The main line continued northwest from Leadore for another 45 miles (72 km), following the broad valley and the Lemhi River downstream through fertile farming and ranching land to the county seat of Salmon. Salmon was the line's terminus, and by far the largest town on the G&P route, with a 1910 population of 1,434.

The only branch line operated by the G&P began at Leadore and headed southeast, following the Lemhi River valley upstream about 19 miles (31 km) to the town of Gilmore, near the upper end of the valley. Gilmore in 1910 was the center of a prosperous silver and lead mining district, and was thus a major source of early traffic for the railroad.