525 Market Street, once known as First Market Tower, is an office skyscraper at the southwest corner of First- and Market Streets in the Financial District of San Francisco, California. The 161 m (528 ft), 39 floor tower was the second largest office building by square footage in the city when completed in 1973. It is owned by the New York State Teachers Retirement System since 1998. It is one of 39 San Francisco high rises reported by the U.S. Geological Survey as potentially vulnerable to a large earthquake, due to a flawed welding technique.