What is the fine-grained topic of the following text: This population explosion has been fueled by the maturing of Las Vegas as the nation's entertainment capital, the rise of Reno as a magnet for multitudes of California expatriates, Salt Lake City's urban corridor development along the Wasatch Range, and Boise's celebrated high-tech economy and hip urban culture. Only return the topic.
Urban development and population growth in Western U.S. cities