The main NWP books all include the line to Cazadero, and Western Railroader had several articles about various parts of it and other NWP items. NG line from Sausalito thru Fairfax & W. Marin, Valley Ford, Occidental, Monte Rio, Duncan's Mills, then up to Cazadero. Bits of r/w are still visible north of Pt. Reyes Station if you know where to look (USGS topo maps can help) even though it was pulled out in the 1930s. Std Gage main line of course ran thru Santa Rosa, with branch west at Fulton to and along the Russian River thru Guerneville connecting with the NG. I was aware from some of those books of an early branch to a sawmill on the flats across from Willow Creek, and a logging line into the Willow Creek area south of the river - but that was very early possibly only before the 1906 earthquake. A woods line to Russian Gulch from that sawmill is quite believable, but identifiable remains after well over 100 years would be surprising.