At the beginning of the 20th century the Southern Pacific had three routes into Portland, Oregon: the West Side branch (built by the Oregon Central Railroad) and the Newberg branch (built by the Portland and Willamette Valley Railway) on the west side of the Willamette River, and the Brooklyn Subdivision on the east side of the river.

[1] The Southern Pacific resolved this issue by constructing a new cutoff linking the three lines.

Beginning at Beaverton, it ran 7.4 miles (11.9 km) southeast to "Cook," on the west side of Lake Oswego.

Beginning at "Wilsonia," on the north side of Lake Oswego, it crossed the Willamette on the Lake Oswego Railroad Bridge, then turned north to run through Milwaukie to Willsburg Junction on the Brooklyn Subdivision.

[5][6] The Beaverton and Willsburg Railroad was conveyed to the Southern Pacific on June 30, 1916.