Anacapia is a geologic province which forms the southern boundary of the Santa Barbara Embayment and the northern limits of an old, often emergent, land mass -Catalinia. It embraces San Miguel, Santa Rosa, Santa Cruz, and Anacapa islands as well as the western part of the Santa Monica Mountains (Reed and Hollister, 1936). A study of the geology and evolution of the Northern Channel Islands, lying as they do on the southern edge of the Transverse Ranges (fig. 1) of California, has long held the interest of natural historians, both geologic and biologic. The Transverse Ranges as a whole form an anomalous feature to the general north-south trending structures of western North America. The Murray Escarp-ment, trending westward 1,900 miles out to sea, is believed to be a structural extension of this continental anomaly. This east-west trend terminates to the east against the great San Andreas fault system and the San Bernardino Range. Not only is it of interest for its obvious structural significance as it is related to one of the great features of the earth's crust, but this transverse feature also has strong biogeographical implications, having roots per-haps as far back as early Mesozoic time. With the progressive provincialization of marine faunas during the Cenozoic (Smith, 1919), these east-west trending mountain ranges, at times partly-submerged, partly emerged, served as the limits on more than one occasion for new biogeographic provinces (Kleinpell and Weaver, 1963), some of which became distinctive and conspicuous life areas in the middle and late Cenozoic. Thus the Transverse Ranges serve as a focal point of considerable significance not only for structural but for biogeographic studies as well. In fact, these two fields, tectonics and chorology, are rather intricately interrelated, though perhaps more directly through intermediate climatological phenomena. 13 The purpose of this paper is to summarize for the Symposium the paleogeographic implications of the available geologic data for the southern fringe of the Transverse Ranges -the Northern Channel Islands. Realizing that members of the Symposium are primarily interested in Cenozoic migratory land routes to the is-lands, it should be stated at the outset that present-day Anacapia offers a paucity of evidence for Cenozoic connections to the mainland. In general, ancient migratory routes are best delineated by the land animals and plants of the time. With but two excep-tions, the late Pleistocene to sub-Recent dwarf mammoths and the Recent biota of the Northern Channel Islands, such organisms are not known to be preserved. The Cenozoic land masses that are needed for faunal migrations to the islands are inferred from: (1) the presence of continental deposits; (2) the absence of de-posits representing major intervals of time, thus permitting the inference that the land was emergent during at least part of the time represented by the hiatus: (3) the fossil and mineralogical composition, texture, and structure of the marine and non-marine sedimentary rocks, which permit ecologic inferences; and (4) the gross structural framework of the province along which any oro¬ genic (mountain building) forces must have operated. The fore-going types of data are available from the literature cited and from recent unpublished work by the authors. Anacapia is an east-west trending physiographic unit with much of its lower elevations flooded by the Recent seas. Its pre-Tertiary, perhaps Mesozoic, origin is faintly reflected in the metamorphic and granitoid rocks of unknown, but pre-Cenozoic, age which are exposed on Santa Cruz Island and in the Santa Monica Mountains. It is dominated by sedimentary and volcanic rocks of Cretaceous to Miocene age and capped by late Pleis-tocene terrace formations. Rock exposures on the islands are notable for their complete lack of Pliocene deposits. The pre-Pliocene shales, sandstones, conglomerates, and volcanics are conspicuous for their lateral variation and discontinuity. Areas of post-Eocene erosion and deposition, especially in Catalinia, appear to have been uplifted and depressed mainly by block fault-ing of the basin and range type, i.e., similar to the basins and ranges common in Nevada (fig. 2). Such deformation began in Oligocene time and continued intermittently through the rest of the Cenozoic Era. Many of the blocks reversed their relative vertical positions during this time (Corey, 1954: Emery, 1954). 1. More information is known than is available to the author, since much data involving the off-shore area are of an industrial and thus confidential nature.