Figure 1. Map showing the sampling locations (and sample sizes) of monarchs used for genomic analyses. The Rocky Mountains (indicated by the schematic black dashed line) are generally believed to form a geographic barrier between eastern and western North American monarchs. Eastern monarchs (indicated in black) migrate to Mexico, where they overwinter at Oyamel forest sites including Sierra Chincua and Cerro Pelón. Western monarchs (indicated in red) migrate to eucalyptus and Monterey Pine groves along the Pacific Coast in California at many sites, including in Big Sur, Oceano, and Carpinteria.