The region of western North America with a Mediterranean-type climate, known as the California Floristic Province (CFP), is a hotspot of endemic plant diversity, largely due to a number of plant lineages that have high diversity within the CFP, but aren’t especially diverse elsewhere. The assumption has long been that the bulk of endemic diversity of these particular lineages in the CFP is due to diversification within the CFP. However, at least some of this endemism may be due to the survival of some species in the CFP whose ranges may have shrunk as southwestern North America became the more arid, desert-dominated region that it is today. Manzanitas (genus Arctostaphylos) are the most diverse woody genus in the CFP, and are seen as emblematic of a within-CFP diversification hypothesis, but interestingly, several species have much larger ranges over extensive areas in western North America. The goal of this study is to evaluate two hypotheses regarding the present-day distribution of these species: (1) these species originated in the CFP and dispersed outward, or (2) they originated well outside of the CFP, and dispersed into the CFP. In this study we sampled multiple populations across the ranges of three such widespread species. Each of these species occur in multiple western US states, and one extends deep in mainland Mexico. We used reduced representation genome sequencing (ddRADseq) data to infer the relationships among populations across the range of each species, and recover the best supported hypotheses about their biogeographic history. Additionally, we examine these data for any hidden structure that may exist that is not recognized by the current taxonomy, and in the case of at least one of the focal species, preliminary findings lend some support for older taxonomy that had treated that species as several distinct species. Understanding the biogeographic history of these widespread species can add valuable context to how lineages like the manzanitas became so endemically diverse in the CFP, and shed light on historical biogeography of other plant lineages in western North America.