The Agua Caliente post office was established in 1886. It was the first post office between Sonoma and Glen Ellen. M. K. Cady built a lavish resort hotel which was famous for its 112-degree natural mineral springs. The resort featured a massive mineral-water swimming pool and drew crowds escaping from San Francisco on the local railway.

An article in an 1889 issue of the Sonoma Index-Tribune read: “During the spring and summer months the Agua Caliente Springs Hotel is crowded with health and pleasure seekers who come to lave in its health restoring water and bask in never failing sunshine and balmy breezes.”

After a devastating fire destroyed the main building in 1915, a new stone hotel, pictured here, was built.