 The project lands have been farmed since the 1840s, but irrigation was difficult due to the lack of a reliable summer water supply.The Berryessa Valley, where the dam and reservoir are located today, was formerly part of Rancho Las Putas, 1843 land grant to José and Sixto Berryessa, for whom the area is named.By the 1860s the "rancho" had been subdivided into many smaller parcels; before damming, the valley was one of California's most fertile agricultural regions, centering on the town of Monticello, with roughly 250 residents.