Ruhnau made many contributions to Southern California's Inland Empire. Since the 1950s he designed many of the region's homes, libraries, banks, schools, churches, and government facilities. Some of his most notable projects include: Riverside City Hall, Riverside County Administrative Center, Sherman Indian High School, downtown Riverside's Main Street pedestrian mall, and the Corona Naval Hospital. Ruhnau also designed a colonial-style mansion in Rubidoux in 1955 for restaurant owner and horse breeder Tiny Naylor that is now the headquarters of the Riverside County parks department.
