In its natural condition the Sacramento Valley was a flood—ravaged region where an inland sea a hundred miles long regularly formed during the rainy season, to drain slowly away by the summer months. Today the Valley is marvelously productive, with a great capital city at its center, but only after a seventy—year struggle to devise and build an intricate thousand miles of levees and drains. Robert Kelley sets that battle within the encompassing national political culture, which produced, through the Republican and Democratic parties, widely diverging ideas about how best to reclaim the Valley from flood. He draws on approaches developed in the field of policy analysis to examine the relationship between American political culture and environmental policy—making. We find that the prolonged controversy over the Sacramento Valley illuminates American decision—making, then and now.