601 California Street, Office skyscraper in Financial District, San Francisco, United States

601 California Street, also called the International Building, is a 22-story, 107 m office tower in San Francisco's Financial District. Its facade alternates light grey horizontal bands with rows of dark rectangular windows, split by a dark vertical channel up the centre. The top 18 floors cantilever 17 feet over the adjacent St. Mary's Square Garage, giving typical floors 12,900 sq. ft. against a 10,000 sq. ft. lot.

The Natomas Company, which controlled American President Lines, formed a subsidiary that bought the 10,000 sq ft lot and built the tower; APL was the primary tenant at completion. By purchasing air rights over the adjacent city-owned St. Mary's Square Garage, the builders cantilevered the top 18 floors 17 feet beyond the property line, making a typical floor 12,900 sq ft, or 129% of the site footprint. The tower received an Honor Award from the American Institute of Architects in 1963.

The building's design reflects how San Francisco transformed its downtown into a center for modern office work during the 1960s. Its clean lines and efficient layout represent the business values of that era.

The tower stands at 601 California Street, where the lower floors cantilever 17 feet over the city-owned St. Mary's Square Garage next door, so the base sits back from the street line. Look for the blue "TUT 601" sign at the lower left of the base. It is a working office building, so plan on viewing the facade and lobby rather than upper floors.

The lot measured only 10,000 sq ft, but the developers bought air rights over the adjacent city-owned St. Mary's Square Garage and cantilevered the top 18 floors 17 feet past the property line. A typical floor therefore covers 12,900 sq ft, 129% of the site footprint. The steel frame used 4,047 tons of steel, fixed with 113,500 A-325 bolts and 9,500 extra-strength bolts.