Human occupations in South America during the late Pleistocene and early Holocene need to be considered from a hemispheric perspective. It is also important to recognize the uniqueness and variety of environmental ecotones found in Northwestern South America. Within the context of the Santa Elena Peninsula in Ecuador, the most complete and earliest record of human occupation comes from the Las Vegas' sites dated between 10,800 and 6,600 BP. The marine faunal record from Early and Late Las Vegas phases reflects a change in the configuration of the littoral caused by tectonic uplift and eustasy, along with other ecological changes. The use of Geographic Information Systems can be effectively implemented in the modeling of ancient coastal configurations.