Whatever it takes. In the early 1960s, construction began on the Oroville Dam. Once the dam was completed, the resulting reservoir flooded the Western Pacific mainline east of Oroville. A new route was created which required civil engineers to use just about every tool in the toolbox. In total, the new route required the construction of five tunnels, three bridges and a horseshoe loop. Here, a heavy westbound grain train rumbles through the 2,922' Tunnel 5 before crossing over Lake Oroville.