A handful of stone knives or scrapers fashioned thousands of years ago were among items turned up Friday, the first day of a weekend “screen-a-thon” for artifacts at Poverty Point State Historic Site.

The round-the-clock event continues until 2 p.m. Sunday, for a total of 50 hours — two more than last year, when 13 volunteers washed the dirt from 16 to 18 boxes of prehistoric artifacts and modern-day construction leftovers.

“We haven’t finished sorting everything we found last year,” said station archaeologist Diana Greenlee, who is supervising the event as part of Louisiana Archaeology Month.

The stone tools were made 3,100 to 3,700 years ago, when the complex of semicircular ridges — the largest, most complicated earthwork of its age in North America — was the region’s top trading site. Its makers moved about 981,000 cubic yards of dirt, basket by basket, to create six concentric C-shaped mounds, the ends of the longest nearly three-quarters of a mile apart.

Friday’s opening also turned up fragments of fired clay cooking balls, dozens of stone flakes chipped off by toolmakers, and a piece of sandstone that obviously had been smoothed by someone though there wasn’t enough of it to tell why, Greenlee said.

Greenlee said last year’s 48-hour event recovered stone tools, fired clay cooking balls and a polished, teardrop-shaped stone plummet that likely was used as a net weight.

Volunteers spread the dirt onto a screen-topped table, then wash it off with a garden hose fitted with a light shower-spray nozzle.

The dirt was excavated for a culvert a couple of years ago. Although it’s from an area where Native Americans are believed to have lived, there was no way to make a precise dig because a driveway had been laid down there sometime before 1938.

The culvert work left behind enough dirt to fill a cube more than 9 yards to a side. Last year’s event went through nearly 4 cubic yards of it.

Gravel that underlay the driveway made up the bulk of what they found, with bits of asphalt, metal and glass. “But there are a lot of artifacts in it,” Greenlee said.

All told, there were 477 pounds of stuff remaining after bucket after bucket after bucket of dirt was washed away.

If volunteers get through as much of the dirt this year, there may not be enough left for a third screen-a-thon.

“Next year may be a sort-a-thon, where we sort all the stuff we got from screening,” Greenlee said.

On the Net:

Poverty Point: http://www.crt.state.la.us/archaeology/POVERPOI/Popo.htm

Louisiana Archaeology Month:

http://www.crt.state.la.us/archaeology/archmonth2009/calendar.asp