Gulf region forming part of the eastern border of El Salvador and composed of a wide variety of coastal environments, including islands, mangrove forests, sand beaches, and rock cliffs. This environment has been subject to relatively little modification and preserves a rich flora and fauna. In the prehispanic past, the Gulf of Fonseca provided the basis for dense human settlement on its islands and mainland fringes, with over 10 major sites presently known. shellmounds are a common type of site, formed over long periods of time by the discard of molluscs that accumulated layer by layer. Available dates for these mouncs range from 1850 BC (currently the oldest absolute date for El Salvador) to the colonial period. Architectural remains are found at some shellmounds and other types of sites, and include mound groups and ruins of early colonial churches. By the Protohistoric period, this area of the Gulf of Fonseca was host to the Lenca ethnic group. Facing the onslought of pirates, the Lenca communites situated on islands were abandoned by the late 17th century, their inhabitants opting to relocate on the mainland. The Gulf of Fonseca's natural resources still support traditional fishing and gathering of molluscs and crustaceans.