From the Monongahela Railroad's incorporation in 1900, the line was equally owned by the Pennsylvania Railroad
and the Pittsburgh & Lake Erie Railroad
, both of which already had branches extending south along the Monongahela River
to Brownsville, Pennsylvania, with the P&LE; on the east bank and the PRR on the west. Construction began on the MRR in 1901 and two years later a twenty seven mile line was opened south of Brownsville, PA, on the east bank of the Monongahela River. The Monongahela expanded a short time later by leasing the Connellsville and Monongahela Railway which tapped the mines located to the south of Brownsville along Dunlap Creek. On July 1st of 1915, the Monongahela Railway was formed following the consolidation of the Monongahela Railroad with the Buckhannon & Northern Railroad, a line that extended south along the Monongahela River to several branches around Fairmont, WV, and a connection with the Baltimore & Ohio Railroad
at Rivesville Junction.
The Monongahela Railway gained more trackage in 1925 by leasing the Scotts Run Railway, a short line that reached across Monongahela County from Randall, WV, to Brave, PA. A year later in 1926, the seeds which would ultimately doom the railroad were sown when the B&O; Railroad gained a 1/3 partnership in the MRY with the P&LE; and the PRR. As part of this deal, the Monongahela gained the following sections of railroad from the involved companies: the Indian Creek and Northern Railroad at Lowsville, WV, which served several mines along Indian Creek; the Chartiers Southern RR, which owned two short branches on the west side of the Monongahela River - one located between Besco, PA, and Mather, PA, with the second between Nemacolin, PA, and Crucible, PA. The PRR also leased two branches to the company: the Ten Mile Run Branch located between the connection with the Chartiers Southern RR's Besco branch and Millsboro; the Crucible Branch which connected with the other section of the Chartier Southern. The Pennsylvania Railroad also extended trackage rights to the Monongahela Railway, connecting the original line with the new additions gained by the transaction: 1) the Redstone Branch between Brownsville and West Brownsville; 2) South from West Brownsville along the west side of the river to Ten Mile Run Jct at Millsboro. The Baltimore and Ohio Railroad extended trackage rights to the MRY from Rivesville Junction up the Paw Paw Branch to the Grant Town mine, although B&O; crews worked the mine and brought trains down the Paw Paw or the RC&P; to Rivesville Junction for interchange. Still not content with the riverbank, the Monongahela expanded the Chartiers Southern's Besco Branch, later the Ten Mile Run Branch, to Waynesburg in 1930, ending the consolidation and building blitz of the first third of the 20th century. During the next three decades the Monongahela Railway was primarily centered on its East Division between Brownsville and Fairmont, with the company's main shops located just south of the former. Coal remained the name of the game through this time period with most outbound coal destined for interchange at Brownsville with the P&LE; or West Brownsville with the PRR. However, this began to change in the years following World War II, when many of the mines located on the East Division began switching to barge transportation, while others were simply worked out and abandoned, resulting in a drastic decline of coal traffic on the railroad.