Geographic variation in the scrub-jays (the Aphelocoma coerulescens species group) has intrigued and confounded ornithologists both before and since Pitelka's (1951) extensive review. In part on the basis of the work of Peterson (1990, 1992), the American Ornithologists' Union (1995) elevated the widespread continental scrub-jays (A. californica, the "Western Scrub-Jay") and the endemic jay of Santa Cruz Island (A. insularis, the "Island Scrub-Jay") to full species rank, restricting the name Aphelocoma coerulescens to the isolated Florida Scrub-Jay.
Components of the Western Scrub-Jay have at times been given full species rank, in the form of a division between birds of the Pacific coast (the A. [c.] californica group of subspecies, hereafter "California Scrub-Jay") and birds of interior western North America (the A. [c.] woodhouseii group, "Woodhouse's Scrub-Jay"); an additional group of subspecies (the "Sumichrast's Scrub-Jay," A. [c.] sumichrasti) occurs on the southern Mexican plateau. Woodhouse's and California Scrub-Jays were treated as separate species most recently by Swarth (1918).