The stone quarries of Rock Creek Park, and the dating puzzle in a charred log

Along some bluffs above Rock Creek and the small streams that feed it, thousands of cobbles show through the dead leaves. They do not look like much, but they are what is left of a prehistoric industry in which ancient Native Americans made hundreds of thousands of stone tools. And the quarries helped settle an argument about when people first lived in North America.

Three rough stone "bifaces" quarried from the banks of Rock Creek. NPS.

A tough stone for a heavy spearpoint

Most of the cobbles are quartzite, a very tough stone that was seldom used in earlier times. About 4,500 years ago, the Native American residents of coastal Virginia and Maryland preferred it for a wide, heavy spearpoint that archeologists call the Savannah River broadspear. Huge numbers of quartzite cobbles were taken from these hillsides and chipped into roughly oval blanks, also called preforms. These were carried to nearby campsites and shaped into finished tools. The quarry sites are covered with millions of fragments of waste stone and many thousands of cobbles that were tested and discarded.

The man who read the debris

The quarries have an important place in the history of American archeology. William Henry Holmes of the Bureau of American Ethnology studied them intensively between 1889 and 1894.

William Henry Holmes. NPS.

The rough oval preforms look something like the Acheulian handaxes of Europe, made between 500,000 and 100,000 years ago. Before Holmes's research, some American archeologists saw the resemblance and concluded that people must have lived in North America in Acheulian times. Holmes worked out how a cobble was chipped into a finished spearpoint and showed that the supposed ancient handaxes were only the middle stages of that process.

Holmes's idea of how a cobble was chipped into a finished spearpoint. NPS.

Holmes's excavations represented the state of the art in late nineteenth-century archeology, and the park says it would be hard to improve on the techniques or reporting even today. Holmes's men dug trenches along hillsides where the cobble beds are exposed, and in some places the debris from ancient quarrying is five feet thick.

Profile of one of Holmes's excavation trenches. NPS.

What survives, and how old it is

Some quarries Holmes studied have been destroyed by the growth of Washington, but others remain intact in Rock Creek Park. Archeologists explored them in 2004. Finds include whole and broken turtleback cores at various stages of completion, half of a large, crude axe that may have been used as a quarrying tool, and the tip of a nearly finished spearpoint.

Broken stone axe found in one of the Rock Creek quarries. NPS.

Archeologists are not sure when, or for how long, the quarries were used. Holmes found no finished spearpoints, whose distinctive style could be dated, and none have turned up since. The best clue is the stone: quartzite was used for tools at many times, but only the Savannah River people used so much that they would have needed quarries this large. Most likely, then, the quarries were used from about 2200 to 1700 BC, dates taken from radiocarbon dating of fireplaces near Savannah River spearpoints at other sites.

Radiocarbon dating became available to archeologists only after 1948, and it needs organic samples, preferably charcoal. That makes one line in Holmes's account tantalizing: Holmes reported that in a side trench there was a good deal of charcoal, and at a depth of about 6 feet a charred log more than 10 feet long and in places a foot in diameter. Holmes kept none of it, not knowing radiocarbon dating would one day exist, so the park's guess at the quarries' age cannot be checked against it.

Sources

• National Park Service, Rock Creek Park, "The Quarries", part of the series Ancient Native Americans in Rock Creek Park (https://www.nps.gov/articles/rock-creek-park-quarries.htm); the park notes its web content is being reviewed with Tribal representatives; rewritten in hubnx's own words.