Greater historical perspective is needed to enlighten current debate about future human responses to higher temperatures and increased precipitation variation. We analyze the impact of climatic conditions and variability on agricultural production in five semi-arid western states. We assemble county-level data on dams and other major water infrastructure; agricultural crop mixes and yields; precipitation and temperature; soil quality, and topography. Using this extensive data set, we analyze the impact of water infrastructure investments on crop mix and yields in affected counties relative to similarly-endowed counties that lack such infrastructure. We find that water infrastructure smooths agricultural crop production and increases the likelihood of a successful harvest, especially during times of severe drought or excessive precipitation.