The Gilmore and Pittsburgh Railroad located in southwestern Montana and east-central Idaho was constructed in 1909 and 1910 from the town of Armstead, MT over the Continental Divide to the town Salmon, Idaho. There was also a branch to the mines in Gilmore, ID. The G&P served mining and agricultural areas in Lemhi County, Idaho and Beaverhead County, Montana. The line was financially backed by the Northern Pacific Railway, and later became its subsidiary. Never financially successful, the G&P ceased operations in 1939, and the railroad was dismantled the following year.

The Gilmore & Pittsburgh bought two "Mikado" type locomotives from the Baldwin Locomotive Works in 1908.

Class 10 (Locobase 13271)

Data from Baldwin Locomotive Works Specification for Engines as digitized by the DeGolyer Library of Southern Methodist University Volume 31, p. 189. See also "Gilmore & Pittsburgh Railroad," Idaho State Historical Society Reference Series 0215 (August 1976) as archived on [external link], last accessed 16 October 2011. Works numbers were 32667-32668 in February 1908.

Locobase 13046 describes a very similar logging Mikado pair built for the McCloud River in 1907. The current pair had a larger grate and firebox and a longer engine wheelbase, but were otherwise essentially identical.

Baldwin had originally sold the pair in this entry to the Missouri River & Northwestern. As the day approached to deliver the engines, however, the MR & N entered foreclosure and the pair was sold to the Rapid City, Black Hills & Western of Armistead, Idaho. But the specs show that the engines were relettered for the Montana-based G & P, indicating RCBH & W's inability to accept them.

Meanwhile, W A McCutcheon secured the backing he needed to build a line that would linking the Oregon Short Line junction at Armistead, Mont over the Bannock Pass to Gilmore, Idaho then on to Salmon, which lay 100 miles to the west and south. The 10 and 11 constituted all of the motive power available.

Within a few years, the G & P (aka the "Get off and Push") had demonstrated its inability to generate a profit and its financial angel, the Northern Pacific, wrote it off. It carried on pulling lead and silver ore trains from Leadore, but an explosion in 1927, the exhaustion of the mines in 1929, the same year as the beginning of the Great Depression sealed its fate.

The Reference Series article said that frequent derailments ultimately led to the line's abandonment: "On the last day [April 30, 1939], with his locomotive derailed three times, the engineer decided to quit. So the Gilmore & Pittsburgh shut down."

Abandoned in 1940 with the rest of the railroad, the two Mikados were broken up for scrap in 1946.