U.S. Interior Secretary Kenneth L. Salazar signs an agreement on Colorado River water usage as Mexican Commissioner Roberto Salmon looks on Tuesday. It amends a 1944 treaty granting Mexico 1.5 million acre-feet of river water yearly. (Associated Press)

U.S. Interior Secretary Kenneth L. Salazar signs an agreement on Colorado River water usage as Mexican Commissioner Roberto Salmon looks on Tuesday. It amends a 1944 treaty granting Mexico 1.5 million acre-feet of river water yearly. (Associated Press)