The zone in which both light and dark males occur on a regular basis is broadest in the north, and extends across the width of the Rocky Mountains and Sierra Madre Occidental ranges. It reaches the Pacific Coast in southern Sonora to northern Sinaloa, roughly between the area of Ciudad Obregón to Culiacán. In the United States, the most diverse array of phenotypes can be found in Colorado and New Mexico. East of the 106th meridian west in southwestern Texas as well as in most of Mexico, almost all males have black backs. Spinus psaltria colombianus (the Columbian goldfinch), east and south of the Isthmus of Tehuantepec, is richer yellow below in males. This, as well as the even yellower S. p. jouyi (the Yucatán goldfinch) from the Yucatán Peninsula and adjacent regions and S. p. witti (the Tres Marías goldfinch) from the Islas Marías off Nayarit require more study, especially as at least the former two seem also to be significantly larger and longer-billed.