The range of the California Halibut, Paralichthys californicus, spans three biogeographic provinces along the coastline of Alto (United States) and Baja (Mexico) California. To assess population genetic structure of the California Halibut, we analyzed mitochondrial cytochrome b sequences from 375 individuals across a large portion of its native range. Nucleotide diversity was consistently low among sampling sites (π = 0.0026 ± 0.0017), while haplotype diversity was consistently high (h = 0.77 ± 0.024). We found that California Halibut were genetically homogeneous across sampled sites with an overall Φst = 0.0030 (p = 0.22). We saw no evidence of genetic discontinuities at two previously recognized marine phylogeographic breaks in the Los Angeles region or across the California Transition Zone at Point Conception. We conclude that California Halibut are genetically homogeneous and experience substantial gene flow, at least over evolutionary time scales.