Another RPO postcard with a photo of a small store. Behind the left window of the store is a large rack of Postcards!
This is the MPOS Narrow Gauge catalog entry for Santa Rosa & Duncans Mills:
Santa Rosa & Duncans Mills, 28 mi, Northwestern Pacific R. R.
note: operated as Short Run of Cazadero & San Fran RPO
984-3-A-1: Santa Rosa & Duncans Mills R.P.O., 29.5, black, 1914-1916, Directional, IV