Exodus from the California Core: Using demographic effectiveness and migration impact measures to examine population redistribution within the Western United States

Increasingly since the 1960s and 1970s, population migration trends within the United States have been driven by the development of a second western population core. The burgeoning concentration of population along the Pacific Coast has fueled the emergence of a significant interconnected system of western metropolitan areas that increasingly rivals the primacy of the long-established northeastern core. During the 1990s the dispersal of population downward within the western urban hierarchy supplanted a much diminished Frostbelt-to-Sunbelt trend to become the most salient aspect of national population redistribution. The Southern California and Bay Area conurbations are serving as the primary pivots fueling the extension of a western urban subsystem. In this study we use county-level IRS matched tax return data and the newly defined Core Based Statistical Area (CBSA) units to explore the recent (1995-2000) flows of U.S. internal migrants within the functional urban system of the western United States. We present maps based on demographic effectiveness and on a new migration impact measure to examine and illustrate the evolving spatial patterns characteristic of current population redistribution across the West.