According to the Ministry of Energy, Northern Development and Mines Ontario, this small rail bridge was part of the "Nepean Junction Mine/Quarry" operational in 1917. Sand stones extracted from the local quarry were used in the construction of the parliament buildings.
As per the 1958 historical aerial image below, you can clearly see signs of the mining operation (cuts thought the side of the hill) as well as a road leading up to the small rail bridge.
1. Loading platform from rail to truck
2. The rails connected to the nearby Nepean
3. Old rail bridge that was repurposed and later abandoned in the woods
Located to the left of the bridge, you can clearly see a small stone staircase leading up to the top of the hill.