This line started out at the turn of the 20th Century as the Tidewater Southern Railroad, an electric interurban that ran from Stockton southwards through Modesto and into Turlock. After the railroad was acquired by Western Pacific and the traffic declined, passenger service ceased.
A few interesting notes of the Tidewater Southern's presence within Modesto. Once passenger service stopped, electric wires along the route were taken down, except for in Modesto proper, which did not allow steam locomotives within city limits. This required the Tidewater Southern to maintain a small fleet of electric locomotives around Modesto, which would then pull entire trains (along with the steam locomotives) through town. This practice was observed long after electric freight trains fell out of favor in the rest of the US, up until diesels starting seeing use in the mid 1940s. In addition, the mainline through Modesto ran right down the middle of 9th Avenue, a major north-south thoroughfare through the center of town. As city traffic increased, the street running was looked upon more and more as a nuisance, as can be expected.
The tracks last saw service in 1999, and in 2000, after the nearby interchange with the UP was completed, the 9th Avenue tracks were paved over, bringing to an end almost 90 years of street running in Modesto, CA.
Thanks to Patrick Patterson for contributing information about this route.