Excavations conducted between 1996 and 2006 at 30 sites on Espíritu Santo and La Partida islands in Baja California Sur, Mexico, reveal a long record of cultural occupation with shell middens located in caves, rockshelters, and on mesa tops. Cultural occupation began during the terminal Pleistocene at the J17 Covacha Babisuri and J69E La Ballena #3 sites and intensi ed during the early Holocene in open mesa and some rockshelter sites. Most cave and rockshelter sites were occupied until the contact period, but mesa sites were apparently abandoned during the middle Holocene. Extensive shell middens were created after 4,500 B.P., rst near mangroves in the backs of bays and later at the entrances to bays.