In the classification of the archaeological cultures of North America, the Archaic period in North America, taken to last from around 8000 to 1000 BC in the sequence of North American pre-Columbian cultural stages, is a period defined by the archaic stage of cultural development. The Archaic stage is characterized by subsistence economies supported through the exploitation of nuts, seeds, and shellfish. As its ending is defined by the adoption of sedentary farming, this date can vary significantly across the Americas. The rest of the Americas also have an Archaic Period. Classifications This classification system was first proposed by Gordon Willey and Philip Phillips in the widely accepted 1958 book Method and Theory in American Archaeology. In the organization of the system, the Archaic period followed the Lithic stage and is superseded by the Formative stage. The Lithic stage The Archaic stage The Formative stage The Classic stage The Post-Classic stage Numerous local variations have been identified within the cultural rankings. The period has been subdivided by region and then time. For instance, the Archaic Southwest tradition is subdivided into the San Dieguito–Pinto, Oshara, Cochise and Chihuahua cultures. Archaic stage in North America Since the 1990s, secure dating of multiple Middle Archaic sites in northern Louisiana, Mississippi and Florida has challenged traditional models of development. In these areas, hunter-gatherer societies in the Lower Mississippi Valley organized to build monumental earthwork mound complexes as early as 3500 BC (confirmed at Watson Brake), with building continuing over a period of 500 years. Early mound sites such as Frenchman's Bend and Hedgepeth were of this time period; all were constructed by localized societies. Watson Brake is now considered to be the oldest mound complex in the Americas. It precedes that built at Poverty Point by nearly 2,000 years (both are in northern Louisiana). More than 100 sites have been identified as associated with the regional Poverty Point culture of the Late Archaic period, and it was part of a regional trading network across the Southeast. Across the Southeastern Woodlands, starting around 4000 BC, people exploited wetland resources, creating large shell middens. Middens developed where the people lived along rivers, but there is limited evidence of Archaic peoples along the coastlines prior to 3000 BC. Archaic sites on the coast may have been inundated by rising sea levels (one site in 15 to 20 feet of water off St. Lucie County, Florida, has been