The Southern Pacific branch that served the wine-growing Napa Valley region extended north/northwest from Napa Junction, through Napa, Yountville, St. Helena and on to Calistoga. As with most branch lines, the traffic volume declined and the SP decided to abandon the line north of Napa; indeed, the rails between St. Helena and Calistoga were pulled up in the 1970s. In the 1980s, some investors purchased the line with the intent of running tourist trains to serve the lineside wineries. After some resistance from some of the wineries, the Napa Valley Wine Train was up and running, using ALCO engines and refurbished passenger cars from the 40s and 50s. The Napa Valley Wine Train still runs, though it stops at only one winery along the way. The train does not reach the northern end of the branch -- the California-Nevada SPV Atlas shows the rails extending a mile or so further north to Krug.
At Calistoga, there is an interesting collection of 1920s and 1930s SP and WP coaches, railway express and observation cars. These cars are located at what was the end of the SP branch. The cars now used as local shops, and while the interiors are modernized, the exteriors were repainted but not significantly modified. Some access doors have been cut into the sides, though. There is also a partally disassembled (possibly vandalized) crossing signal.
Thanks to Mike Palmer for contributing information about this route.