Based on 1890 returns, the U.S. Bureau of the Census declared the frontier closed. In
1893, Frederick Jackson Turner began expressing his well-known thesis regarding the importance of
the frontier in America's growth and development. Freely-available land depleted over time and
frontier culture changed a great deal; however, one important aspect of the frontier remained--people
continued moving west. It was not until 100 years later, during the 1990s, that net migration to the
West ceased. Why? That is the question addressed in this paper, which uses modified gravity models
of interstate migration based on 1970, 1980, 1990, and 2000 census data in combination with
seemingly unrelated Tobit regressions to demonstrate that the concentration of the foreign born in the
West has been an important factor in the native-born population departing the West and tending to
not move there.