Between 2020 and 2050, all states comprising the Mountain Mega-Region (MMR—Arizona, Colorado, Nevada, New Mexico, and Utah) will be among the top 10 fastest growing U.S. states. They also have among the nation’s largest shares of land area in federal, state, public, and tribal land ownership. This has led to concentrations of populations in their metropolitan areas. Indeed, in 2020, the metropolitan areas of more than one million residents—Albuquerque, Las Vegas, Phoenix, Salt Lake City, and Tucson—comprise more than 70% of their states’ populations. With rapid growth combined with land constraints, many of these metropolitan areas are using rail transit systems to help meet transportation needs while also influencing development patterns in intended ways. If they are effective, these rail transit systems will: (a) create commercial real estate rent premiums; (b) attract jobs; and (c) attract households to areas near rail stations. We report the effectiveness of MMR rail transit systems in each of these respects. We also present a surprise: Contrary to conventional wisdom, it is households with children that locate closest to rail stations than single persons and childless households. We reason that improved planning is needed to meet the market demand for development throughout the half-mile circle around transit stations in the MMR’s metropolitan areas. If this can be done, all development in these MMR metropolitan areas may occur near rail transit stations.