LOTHIAN, Md. — For weeks, Al Luckenbach puzzled over the bones surfacing in the pit atop the Patuxent River bluff here. They were hard to identify: fragments and shattered splinters, unlike the intact animal bones heaped in the nearly 9,000-year-old feast site down the hill.

Then the scrape of a trowel tip uncovered a human tooth in the dirt among the crushed pottery and broken spearheads. Two more followed, and a startling realization emerged with them: the bones on the hilltop were human, with marks suggesting they were deliberately smashed as part of a prehistoric ritual.

Since that discovery last year, the spot known as Pig Point has become a tantalizing window into prehistoric gatherings on the hilltop thousands of years ago. While burial sites are relatively common, ancient ceremonial sites as deep and well preserved as the one believed to be atop Pig Point are extremely unusual....