Not available – first paragraph follows: Most of the San Joaquin Valley has been farmed in one fashion or another for more than a hundred years The Valley trough was generally dry-farmed until deep-well turbine pumps were developed in the 1930s and 1940s and irrigation became common. Even though much of the land was in production, it was not irrigated every year: there was some pattern of rotation, such as dry-farming for one year, irrigation for two, and fallow for one. Now, almost 5 million acres of agricultural land on the Valley floor are irrigated.