Disaster and Demographic Selection: The 1906 San Francisco Earthquake and Urban Area Composition

Abstract

Urban disasters reshape cities not just physically but demographically. Using U.S. Census full-count data from 1900 and 1910, we examine how the 1906 San Francisco earthquake and fire transformed the composition of the San Francisco County population. Employing a descriptive difference-in-differences comparison with Los Angeles County and King County (Seattle) as controls, we document three striking patterns. First, San Francisco County became substantially more male after the disaster: the male share of the working-age population increased by 7.4 percentage points relative to comparison counties, as men arrived for reconstruction while families departed. Second, the workforce "deskilled"—mean occupational scores fell by 1.66 points relative to comparison counties, driven by the departure of skilled operatives and the influx of laborers and craftsmen for rebuilding. Third, San Francisco's foreign-born share declined more sharply than in comparison counties: among working-age adults, San Francisco fell by approximately 3.5 percentage points while comparison counties fell by only 0.9 percentage points, a relative difference of 2.6 percentage points. Given that we have only three geographic units, we present these as descriptive contrasts rather than formal statistical tests. These findings demonstrate that major disasters can reshape urban populations through selective migration.