Question: Which American railroad, located in Southwestern Montana and Idaho, was backed by the Northern Pacific Railway?

full_context: Document 1: Western Pacific Railroad (1862–70): The Western Pacific Railroad was formed in December, 1862, by a group led by Timothy Dame and including Charles McLaughlin and Peter Donahue, all associated with the San Francisco and San Jose Railroad, to build a railroad from San Jose north to Vallejo's Mills (mouth of Niles Canyon, later Niles, now part of Fremont), east through Niles Canyon, north to Dublin/Pleasanton, east through the Livermore Valley, and over Altamont Pass to Stockton, then north to Sacramento, with the plan that the transcontinental railroad would follow the Western Pacific to San Jose and then the San Francisco and San Jose to San Francisco. In October, 1864, the Central Pacific Railroad assigned all the rights of the Pacific Railway Acts of 1862 and 1864 to the Western Pacific for the route between Sacramento and San Jose, including land grants. In 1866, the first twenty miles from San Jose had been completed when funding problems halted construction within Niles Canyon. Part of the difficulty was that federal land grants were not available where Mexican land grants had previously been made.
Document 2: Armstead, Montana: Armstead is a former community in Beaverhead County, Montana, United States, about 21 mi south of the county seat of Dillon. It was named after miner Harry Armstead. Armstead was located in a narrow valley of the Beaverhead River, near the mouth of Horse Prairie Creek. The town was a station stop on the Union Pacific Railroad line from Idaho Falls, Idaho to Butte, Montana. There was a post office in Armstead from 1907 to 1962.
Document 3: Montana Railroad: The Montana Railroad was an American railroad built and operated between the towns of Lombard and Lewistown, Montana, a distance of approximately 157 miles. The railroad connected with the national railway network via a connection with the Northern Pacific Railway at Lombard. The Montana Railroad line was constructed between 1895 and 1903, and operated independently until 1908, when it was acquired by the Chicago, Milwaukee, St. Paul and Pacific Railroad ("the Milwaukee Road"). The railroad was colloquially known as "the Jawbone", because of the contrast between the promising statements of the line's promoters and the company's perennially-weak financial position.
Document 4: Great Northern Railway (U.S.): The Great Northern Railway (reporting mark GN) was an American Class I railroad. Running from Saint Paul, Minnesota, to Seattle, Washington, it was the creation of 19th-century railroad entrepreneur James J. Hill and was developed from the Saint Paul & Pacific Railroad. The Great Northern's (GN) route was the northernmost transcontinental railroad route in the U.S.
Document 5: SS Northern Pacific (1914): SS "Northern Pacific was built as a passenger ship at Philadelphia by William Cramp & Sons under supervision of the Great Northern Pacific Steam Ship Company for the Spokane, Portland and Seattle Railway Company. "Northern Pacific", along with sister ship "Great Northern" , were built to provide a passenger and freight link by sea between the Great Northern Railway Lines and Spokane, Portland and Seattle Railway terminal at Astoria, Oregon and San Francisco beginning in spring of 1915. The ship was acquired on 17 September 1917 for use as a transport ship for the United States Navy during World War I, commissioned USS "Northern Pacific and later, after transfer to the United States Army, as the Army transport USAT "Northern Pacific". She was destroyed by fire in 1922.
Document 6: Northern Securities Company: The Northern Securities Company was a short-lived American railroad trust formed in 1901 by E. H. Harriman, James J. Hill, J.P. Morgan and their associates. The company controlled the Northern Pacific Railway; Great Northern Railway; Chicago, Burlington and Quincy Railroad; and other associated lines. It was capitalized at $400 million, and Hill served as president.
Document 7: Northern Pacific Depot (Aitkin, Minnesota): The Northern Pacific Depot in Aitkin, Minnesota, United States, is a brick passenger depot built on the Northern Pacific Railway mainline in 1916. The rail line is now part of the BNSF Railway. The depot symbolizes the importance of the railroad in Aitkin's growth and development.
Document 8: Chicago and North Western Transportation Company: The Chicago and North Western Transportation Company (reporting mark CNW) was a Class I railroad in the Midwestern United States. It was also known as the North Western. The railroad operated more than 5,000 miles (8,000 km) of track as of the turn of the 20th century, and over 12,000 miles (19,000 km) of track in seven states before retrenchment in the late 1970s. Until 1972, when the company was sold to its employees, it was named the Chicago and North Western Railway (or Chicago and North Western Railway Company).
Document 9: Northern Transcon: The Northern Transcon, a route operated by the BNSF Railway, traverses the most northerly route of any railroad in the western United States. This route was originally part of the Chicago, Burlington and Quincy Railroad, Northern Pacific Railway, Great Northern Railway and Spokane, Portland and Seattle Railway systems, merged into the Burlington Northern Railroad system in 1970.
Document 10: Denver, South Park and Pacific Railroad: The Denver, South Park, and Pacific Railroad (later called the Denver, Leadville and Gunnison Railway) was a historic narrow gauge railroad that operated in Colorado in the western United States in the late 19th century. The railroad opened up the first rail routes to a large section of the central Colorado mining district in the decades of the mineral boom. The railroad took its name from the fact that its main line from Denver ascended the Platte Canyon and traversed South Park. Founded in 1872 by Colorado Governor John Evans, the company was purchased by the Union Pacific Railway in 1880, though it continued to be operated independently. The line went bankrupt in 1889 and was reorganized under the new moniker the Denver, Leadville and Gunnison Railway. When the Union Pacific went bankrupt in 1893, the DL&G lines went into receivership and were eventually sold to the Colorado and Southern Railway. In the first half of the 20th century, nearly all the company's original lines were dismantled or converted into . The last train to run the old DSP&P tracks was from Como, Colorado on April 11, 1937. A section of the standard gauge line between Leadville and Climax is still operated as a passenger excursion railroad called the Leadville, Colorado and Southern Railroad. At its peak the Denver, South Park and Pacific Railroad had 335 mi of narrow gauge line, making it the largest narrow gauge railroad in the state of Colorado.
Document 11: Butte County Railroad: The Butte County Railroad was a 31.5 mi class II railroad that ran from a connection with the Southern Pacific Railroad at Chico, California to the Diamond Match Company lumber mill at Stirling City. The railroad operated from 1903-1915 and then became the Southern Pacific's Stirling City Branch. From 1915 until abandonment in the 1970s the line was operated as the Southern Pacific's Stirling City Branch. The Chico and Northern Railroad was a non-operating subsidiary holding company of the Southern Pacific Railroad that was created to acquire a 32.31 mile line from Chico - Stirling City from the Butte County Railroad. Upon acquiring the line, Chico & Northern immediately leased the line back to the Butte County Railroad. The Chico & Northern was dissolved into Southern Pacific in 1912 and never operated any of the line.
Document 12: Gilmore and Pittsburgh Railroad: The Gilmore and Pittsburgh Railroad (G&P), now defunct, was an American railroad located in southwestern Montana and east-central Idaho. Constructed in 1909 and 1910 between the towns of Armstead, Montana, and Salmon, Idaho, 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.
Document 13: Saint Paul and Pacific Railroad: The Saint Paul and Pacific Railroad (also known as the St. Paul & Pacific Railroad and the SP&P) was a shortline railroad in the state of Minnesota in the United States which existed from 1857 to 1879. Founded as the Minnesota and Pacific Railroad, it was the state's first active railroad. It went bankrupt, and the state changed its name to the Saint Paul and Pacific Railroad. The SP&P went bankrupt as well. It was taken over by James Jerome Hill and others, who used the railroad as the basis for building the Great Northern Railway.
Document 14: Lac La Belle and Calumet Railroad: The Lac La Belle and Calumet Railroad was an American, narrow gauge railroad that operated in the Keweenaw Peninsula, or the extreme northern Upper Peninsula of Michigan. The line ran between a stamp mill at Lac La Belle and two copper mines, the Mendota and the Delaware, from 1883 to 1888, when poor economic conditions forced the line's closure. The defunct company and its tracks were later purchased by the Copper Range Company, which converted the line to standard gauge and changed the railroad's name to the Keweenaw Central. This company failed in 1917, and the former Lac La Belle and Calumet tracks were removed in 1918.
Document 15: Northern Pacific Railway: The Northern Pacific Railway (reporting mark NP) was a transcontinental railroad that operated across the northern tier of the western United States, from Minnesota to the Pacific Northwest. It was approved by Congress in 1864 and given nearly 40000000 acre of land grants, which it used to raise money in Europe for construction.
ground_truth: Gilmore and Pittsburgh Railroad