Archaeologists have hit pay dirt at Poverty Point, La.

Using a variety of advanced non-intrusive instruments, an Army Corps of Engineers team has for the first time geophysically found and mapped "subsurface architecture and cultural features" that were constructed by the area's early residents, the Poverty Point Culture (about 1730 to 1350 B.C.).

Tad Britt, a graduate student at the University of Illinois at Urbana-Champaign, said his team produced "very accurate maps" of man-made ridges and trenches just below the surface of the ground. They surveyed ridges 1-5 of the southwest sector of Macon Ridge, above the Mississippi River floodplain.

The maps document the precise arrangement of and spacing between the concentric semicircular ridges and trenches. Ridges range from 65 to 115 feet apart, with the outermost being three-quarters of a mile in diameter -- all "indicative of a carefully designed and well-executed plan," Britt said.

The earthworks may have been used as a marketplace, and three circular anomalies found on the ridges may be post holes for roundhouses, built at different times. "The site was occupied for almost 1,500 years and was continually being modified. What remains is a palimpsest of human occupations."

One of the goals of the project, in addition to collecting data about the hidden features, was to determine which non-invasive instruments worked best at detecting subsurface anomalies "indicative of cultural features," Britt said. Magnetic field gradiometry and electrical resistivity proved most successful. In addition to Britt, the principal investigator, team members were Michael Hargrave and Janet Simms; all three work for the Corps' Engineer Research and Development Center.

Previous non-invasive surveys by other archaeologists were inconclusive. Similarly, traditional excavations at the site over the past 100 years have failed to provide "a clear understanding of the nature, distribution and density of archaeological features such as pits, hearths, post holes and other structural remains," Britt said.

Despite the latest discoveries, the huge, 400-acre site remains "unique and enigmatic" -- much of the current understanding regarding its evolution and its inhabitants' subsistence, lifeways and social order "still speculative and largely based on data recovered from surface finds and limited test excavation."

Nevertheless, Poverty Point is a critical archaeological site in the United States and a textbook case for the evolution of a non-agricultural, socially complex culture.

Elsewhere during the same time period, American Indians lived "a much simpler lifestyle as hunter-gatherers," Britt said. "There are some exceptions, all in Louisiana, that predate Poverty Point by a couple thousand years. But they do not possess the level or scale of the Poverty Point site."

Recent archaeological studies in the area indicate that the earliest mounds in the Americas also are in northeast Louisiana. Those mounds are earlier than the Olmec mounds in Mexico, he said, and even the Egyptian pyramids at Giza.