O'Shaughnessey Dam

Construction of the dam at Hetch Hetchy began almost immediately after President Woodrow Wilson signed the Raker Bill into law. The valley floor was cleared of all timber, roads and railroads were constructed into the valley, the dam site at the mouth of the valley was blasted back to bedrock, the process of pouring layer upon layer of concrete commenced, tunnels for the pipeline to the San Francisco Bay area drilled, and construction of power plants begun. Initial construction took nine years. Dedication of O'Shaughnessey Dam - named after the city's and the project's chief engineer, Michael O'Shaughnessey - took place on July 7, 1923.

To Start You Thinking

1) Study the geography and geology of the Hetch Hetchy Valley pictured above in a 1977 aerial photograph. Comment on the features that lent the site to dam construction and the existence of a large reservoir.

2) Review the series of slides showing scenes from the construction of the dam. Carefully study the slides you and your group were assigned addressing the questions on the Photo Analysis Guidelines sheet. Be prepared to present your analysis of and questions about each slide as part of a chronological discussion of the dams' construction.


image from Manuel Dias, "Hetch Hetchy, 1977" available at Calishere

Last modified in June, 2019 by Rick Thomas