This dataset contains genomic records from 184 California Gnatcatchers (Polioptila californica) collected at 18 sites in southern California (USA), 13 sites in Baja California (Mexico), and 17 sites in Baja California Sur (Mexico). Genomic markers were generated from ddRAD loci (Peterson and others, 2012) and analyzed using the Stacks v2.53 (Catchen and others, 2013) pipeline. The genotypes for all samples are provided in a VCF file with 84,125 independent loci and 7 percent missing data. A companion file is provided with sample names and occurrence designations. These files may be opened and edited in a text editor program, such as Notepad (PC) or BBEdit (Mac). The .vcf file can be loaded into the Stacks population program (Catchen and others, 2013) to calculate genetic diversity statistics, or loaded into R, using vcfR (Knaus and Grunwald, 2017), for further analysis. References: Catchen J., Hohenlohe P.A., Bassham S., Amores A., Cresko W.A. Stacks-an analysis tool set for population genomics. Molecular Ecology. 2013; 22:3124-3140. Knaus, B.J, Grunwald N.J. vcfr: a package to manipulate and visualize variant call format data in R. Molecular Ecology Resources. 2016; 17:44-53. Peterson B.K., Weber J.N., Kay E.H., Fisher H.S., Hoekstra H.E. Double Digest RADseq-an inexpensive method for de novo SNP discovery and genotyping in model and non-model species: PLoS ONE. 2012; 7:e37135.