Technically, desert are areas that receive 10 or fewer inches of rainfall a year. While many people think of them as devoid of life, several major American cities, such as Phoenix and Las Vegas, are located in deserts. The following site provides information on deserts. Another source of information is the individual parks that are located in deserts, which can be found by using the Geology of the National Parks web site, listed in the Regional Geology section of this guide.