The area known as Bonsall was originally called
Mount Fairview and had a post office by that name from December 28, 1871, to December 28, 1880. It received a post office in 1881 under the name
Osgood, after
California Southern Railroad chief engineer Joseph O. Osgood; the renaming was supposedly an unsuccessful attempt to convince Osgood to build the railroad through the
San Luis Rey River Valley (the rail line eventually followed the
Santa Margarita River instead). Following a contest, the town was renamed Bonsall in 1890, after local minister James A. Bonsall. ==Geography==