The rich biota of islands in the Gulf of California has attracted the efforts of naturalists and research biologists for nearly a century (Case and Cody 1983). Mammals are among the better-studied groups and have been the focus of biogeographical and evolutionary research (e.g., Burt 1932; Huey 1964; Banks 1967; Lawlor 1971, 1983). Much of this work focused on fauna of large islands in the southern Gulf and Midriff region (e.g., Vaughan and Schwartz 1960; Gill 1981; Smith 1992), whereas less is known of the distribution of mammals on the dozens of small islands that surround the Baja peninsula. These small islands may be particularly important for studies of island biogeography because island area strongly influences resource availability and the probability of extinction and colonization of insular populations (Mac Arthur and Wilson 1967; Whittaker 1998). Here, I provide new records of the distribution of mammals on a series of small islands in the central Gulf of California. These data were collected as part of a larger research effort aimed at understanding the dynamics of island food webs (Polis and Hurd 1996; Polis et al. 1997; Stapp et al. 1999).