For a pretty detailed topographic map showing the Danville Branch, I would recommend going to the USGS site here:
[
geonames.usgs.gov]:::::
Search for maps named Concord, under California of course. Also select either "Historical" or "All" for types of maps. They show Concord maps dated 1897, 1915, and 1959, each with multiple printing dates. I selected one of the 1915 maps, and it shows the branch in excellent detail to the edge of Danville. It should run over on the next map, Mt Diablo, but neither of the 2 editions they have, 1898 and 1943, show the SN branch.