The Richardson brothers had big plans to build storage dams on the Yaqui to generate electric power and furnish water to a network of canals capable of irrigating 300,000 hectares. The Mexican Revolution and World War I destroyed their enterprise but the dream of transforming the Yaqui Valley into a vast grid of irrigated agribusiness bore fruit in 1952, when the Mexican government completed Alvaro Obregon Dam at Oviachi forty miles away. Along with dams upriver, the Oviachi reservoirs controlled flow along the lower Rio Yaqui and eventually channeled its water into three major canals that irrigate nearly 600,000 acres in the Yaqui Valley.

Cuidad Obregon, a city of more than 500,000 people arose to service the largest irrigation district in Sonora. Recognizing the Yaqui Valley's importance, the Rockefeller Foundation established a wheat-breeding station on the outskirts of Obregon. This station became one of the hearths of the Green Revolution, that controversial program that dramatically increased wheat production--all of it dependent upon high inputs of chemical fertilizers and pesticides--around the world.

North of the Yaqui Valley, advances in pump technology after World War II allowed other coastal irrigation districts to bulldoze desert plains and convert them into wheat and cotton fields. The largest was the Costa de Hermosillo where, at its height, 887 pump-powered wells regurgitated water onto more than 100,000 hectares. But discharge exceeded recharge by 250 percent. As water tables plummeted and salt water intruded from the Gulf of California, the Mexican government finally stepped in and halved the amount of water that could be pumped. Other farmers switched from relatively low-value crops like cotton to high-value, high-risk crops like brandy grapes, citrus, garbanzo beans, and vegetables destined for US markets.

Because of these developments, Sonora's demographic, political, and economic center of gravity shifted from the serrana to the coast during the twentieth century. Dam-building and groundwater pumping enable capital-intensive agricultural districts to plow under the great mesquite bosques (forests) west of Hermosillo and desert ironwood plains around Caborca. Those twin pillars of modern water control also allowed older cities like Hermosillo... to expand and entirely new cities ... to spring up like an industrial flower south of the dry channel of the Rio Yaqui. ... Hermosillo already experiences severe water shortages during dry seasons and dry years. Groundwater districts like Caborca and the Costa de Hermosillo are contracting painfully as aquifers drop and pumping costs escalate. Even the Yaqui Valley with its huge reservoirs faces an uncertain future as the North American Free Trade Agreement (NAFTA) reshapes Mexican agriculture.

In Arizona, the future of agriculture is held hostage to urban growth. During the early twentieth century, the newly created Reclamation Service (precursor of the US Bureau of Reclamation) erected the Roosevelt Dam in 1903 on the Salt River east of Phoenix and turned the Salt River Valley into one of the largest agricultural centers in the Southwest. And when a British embargo on long-staple industrial cotton during World War I triggered Arizona's cotton boom, commercial agriculture spread across the saltbrush and cresosote bush flats between Phoenix and Tucson. Arizona became one of the leading cotton producers in the World.

But World War II and the postwar boom thrust Arizona from the Era of Extraction into the Era of Transformation, turning an overwhelmingly rural state into an overwhelmingly urban one. Thousands of acres of citrus and cotton sprouted subdivisions and malls as Phoenix and its satellites sprawled in to a metropolis of more than 2,500,000 people by 1995. Metro Tucson approached 750,000. By the time the Central Arizona Project (CAP)--a farmers dream since the 1920's--reached Maricopa, Pinal, and Pima counties, many farmers could not afford its water. The CAP became one more bargaining chip in the water game, that escalating contest that pitted relentlessly expanding cities against farmers, miners, and Indian nations.