The damming of Hetch Hetchy Valley in Yosemite National Park is widely seen as a watershed event in American environmental history. Passionately opposed by naturalist John Muir and his ardent supporters, the massive undertaking succeeded largely through the efforts of John R. Freeman, one of the most important, influential, and politically adroit engineers of the Progressive Era. In The Man Who Dammed Hetch Hetchy, Donald C. Jackson focuses on Freeman to offer a nuanced account of how the City of San Francisco won the right to transform the bucolic valley into a municipal water supply reservoir that, a century later, continues to serve millions of Bay Area residents. Central to Freeman's work for San Francisco from 1910 to 1913 was his design of a high-pressure aqueduct projected to deliver 400 million gallons of water per day to the Bay Area and generate more than 150,000 horsepower of electricity. Beyond crafting an extensively illustrated 42 -page report detailing his design, he also worked - and succeeded - as a political advocate lobbying for Congressional approval of the project. Jackson draws on a wealth of correspondence, reports, and other documents, including Congressional records, to highlight Freeman's contention that the Hetch Hetchy project would not just provide copious quantities of water and power, but would also enhance the Sierra Nevada environment and increase tourist access to the northern reaches of the national park. His self-avowed goal was not to tear down or destroy Hetch Hetchy but to utilize the valley for the greater public good and to create a system that would serve the city for decades if not centuries to come. Portraying Freeman for the first time in all his provocative complexity, The Man Who Dammed Hetch Hetchy is at once a deeply researched, richly detailed biography and social history and a compelling reinterpretation of a pivotal moment in US environmental culture.