1. Human Interaction with the Environment

2. Downstream view of the convergence of the west branch of the Santa Cruz River in Tucson. Between 1904 and 1981 deterioration of the riparian vegetation is evident due to groundwater depletion and urbanization,

10. Hoover dam on theColorado River, on the border between the U. S
Hoover dam on theColorado River, on the border between the U.S. states of Nevada and Arizona. It was constructed between 1931 and 1936 during the Great Depression It provides irrigation and hydropower