This was a branch of the Tidewater Southern Railway (a subsidiary of the Western Pacific) and was built in March of 1918. This 6-mile branch extended south from Manteca Junction on the Tidewater Southern to the city of Manteca itself. The area around Manteca is mainly agricultural; the line at one time served no less than 8 fruit-packing sheds in Manteca proper. While a freight-only branch, WP accounting files indicate that this branch was originally electrified; the overhead wires were removed in 1930.
When the WP was acquired by the Union Pacific in 1982, the Tidewater Southern was also merged into the UP.
The branch was likely abandoned in the early 1990s, when all former WP and SP lines were consolidated with the UP. A customer in South Manteca had its siding connected with the former SP main line when the TS line was abandoned. Today, a portion of the line in downtown Manteca is used as the Tidewater Bikeway.
Thanks to Mike Palmer for contributing information about this route.