Update Feb 2021: See additional new images of the Sunnyside Powerhouse.
Sunnyside played an important role in the development of the first electric streetcar in San Francisco. Before the enterprise was initiated in 1890 by streetcar-railway engineer John Wesley Hartzell, with financial backing from millionaire real-estate speculator Behrend Joost, horse-powered and cable-driven streetcars were the norm. Soon the newly introduced technology would power many of SF’s many privately-held transit lines. But the San Francisco and San Mateo Railway was the first electric railroad in the city.
Central to the enterprise was the Sunnyside Powerhouse, located on the then unbuilt flatiron-shaped block between Monterey, Circular, and Baden.