Only in the last few years have high-resolution paleoclimatic data become available from coastal southern California. Recent research in the California Channel Islands, drawing on some of these data, attributes settlement disruptions, disease, and violence to maritime subsistence distress attendant to elevated sea temperatures in the period from A.D. 1150 to 1300. A broad range of paleoenvironmental, archaeological, and human osteological data suggest that these stress indicators are more convincingly correlated with severe late Holocene drought episodes during a portion of the medieval climatic anomaly (ca. A.D. 800 to 1400). Based on these data, cultural changes in coastal southern California, including violence, declining health, and emergent social complexity, are similar to events documented in the American Southwest. Cultural adaptations in both regions appear to have been responding to persistent drought conditions during the late Holocene.