 However, with some 1,200 wells in operation by the 1920s, the local wetlands began to disappear as the depth to groundwater increased.Dry farming gradually replaced irrigated farming as it became more expensive to drill new deeper wells.The Irvine Ranch also imported surface water from Santiago Creek starting in the 1930s, when it constructed Santiago Dam to form Irvine Lake, the largest body of fresh water in Orange County.