George Mountain was born in Quebec City in 1860, and joined the Canada Atlantic Railway in 1881 as assistant under Walter Shanley. He became the chief engineer of the CAR when Shanley retired in 1887.
As chief engineer, he was responsible for overseeing the location and construction of the Ottawa, Arnprior and Parry Sound Railway, as well as the St Lawrence crossing at Coteau and elevators and town at Depot Harbor.
He resigned from the Canada Atlantic in July 1904 to take the position of chief engineer for the Board of Railway Commissioners. [Engineering and Contract Record, Vol 25, No. 3. Hugh C MacLean Ltd, Winnipeg. January, 1911. p57]