My "What If" railroad takes up the history in 1906. (Although, if I had the money and time, I would build them as they were.)
The NCNG, successfully lured business expansion into the region by buying out the land, buildings, and equipment of the standard gauge California Midland shortly after the San Francisco earthquake. This gave the NCNG a connection with the SP at Colfax and a connection with the then Sacramento Northern, later Western Pacific, at Marysville.
Discussions over converting the narrow gauge track to standard soon followed - it took 3 narrow gauge cars to fill one standard gauge car (see photo). Also, it would save time and money by eliminating transfer sheds used to move merchandise between standard
and narrow gauge cars.
By the First World War, all track was standard gauge and the railroad took over the name California Midland.
The Nevada County Traction Company became an inter-city commuter subsidiary of the California Midland. Currently, the year modeled is 1952 - steam locomotives are very much alive, but diesel locomotives are starting to move in.
If you are interested, check my page links above to see my progress.