What was the most important resource that allowed the Western desert states to expand in the 1960s?

The most important resource that allowed the Western desert states to expand in the 1960s was water, particularly from the Colorado River and various aqueduct systems. The construction of large-scale water projects, such as the Hoover Dam and the Central Arizona Project, facilitated irrigation and urban development, supporting agriculture and population growth. This influx of water made it possible for cities like Las Vegas and Phoenix to thrive in otherwise arid conditions, driving economic expansion and attracting new residents.