The Petaluma and Santa Rosa Railroad was incorporated in 1903 to establish interurban and freight service between its namesake towns. The track was laid in 1904 and service started soon after. In 1928, the P&SR was purchased by the Northwestern Pacific Railroad, with cessation of trolley service coming in 1933. The line was abandoned in 1984, with only remnants preserved in Petaluma to serve local industries.

An interesting story that involves the P&SR was a mild battle between the it and the Northwestern Pacific Railroad in 1905 involving a grade crossing in Santa Rosa. The NWP had already established service between Petaluma and Santa Rosa, so when the P&SR tried to establish service between the same two cities, the NWP protested by preventing the P&SR from crossing their line in Santa Rosa. When the P&SR attempted to install the crossing in a "sneak attack", the NWP was already prepared with awaiting steam locomotives ready to blast boiling hot water on any trespassers. At one time during the battle, the P&SR actually laid their tracks over those of the NWP, a solution that didn't last long. And for a time, when an eastbound P&SR trolley would reach the crossing, the passengers were required to disembark and board another trolley on the other side of the crossing to continue eastbound, and vice-versa. A court ruling finally allowed the P&SR to install their crossing, putting an end to the 3-month conflict.