Crystal Springs Dam

About

Crystal Springs Dam is a concrete gravity dam constructed across the San Mateo Creek in San Mateo County, California, United States. It impounds water in a rift valley created by the San Andreas Fault to form the Crystal Springs Reservoir. The dam is located about 1,100 feet (340 m) east of the fault. It is owned and operated by the San Francisco Public Utilities Commission, and stores drinking water for the City of San Francisco. The current dam is 145 feet (44 m) high with a crest length of 600 feet (180 m).

It was the first mass concrete gravity dam built in the United States. Upon its completion in 1889, it became the largest concrete structure in the world and the tallest dam in the United States. A 2024 review by American Society of Civil Engineers (ASCE) and the Institution of Civil Engineers in Great Britain indicated that it is likely the oldest mass concrete dam in the world. Construction techniques used at the dam, including washing aggregate and staggered joints, influenced the development of future gravity dams, such as Hoover Dam and Grand Coulee Dam. In December 2023, it was recognized as a National Historic Civil Engineering Landmark by the ASCE.