Until just a few decades ago, Nevada did not have any large cities at all.
However, with the establishment of Las Vegas in the middle of the 20th century, and its subsequent rapid growth, Nevada is quickly catching up to more urbanized states. Between 2000 and 2006, Nevada’s population grew by almost 25% (http://quickfacts.census.gov/qfd/states/32000.html). At the same time, neighbor Arizona’s population increased by 20% (http://quickfacts.census.gov/qfd/states/04000.html). Perhaps the Las Vegas-Los Angeles-Phoenix triangle will be the Megalopolis of the 21st century.