If the California Islands were marginal for human settlement, why were several of them occupied more or less continuously since Terminal Pleistocene or Early Holocene times? The earliest human history of California's Islands is clouded by sea level rise, coastal erosion, dune building, and differential research intensity. Nonetheless, Paleocoastal sites are abundant on the Northern Channel Islands and Cedros Island, suggesting that they were optimal habitat for early hunter-gatherers, with ample food, freshwater, mineral, and other resources to sustain permanent settlement. Worldwide on islands where late Pleistocene or early Holocene human colonization occurred, climate shifts and massive landscape changes caused by postglacial sea level rise require detailed reconstructions of paleogeography and paleoecology to assess the potential productivity or marginality of islands or archipelagos.