Obsidian Cliff: Humanity’s Tool Shed for the Last 11,500 Years

The geochemical fingerprint of the cliff’s volcanic glass has been found all around the West, as well as in Canada. Area tribes “all knew about it, all the archaeological sites in Montana that are important have some form or another of obsidian, and most of it comes from this place — Obsidian Cliff,” Dr. MacDonald said. “All of the tribes in Montana, Wyoming and Idaho were going out of their way to get it.”

One lingering mystery of Obsidian Cliff stumps scientists to this day: How, some 2,000 years ago, did hundreds of pounds of obsidian wind up at what is now Hopewell Culture National Historical Park in Ohio, about 1,700 miles east of Yellowstone. Researchers do not know if the material traveled through trading networks or was gathered by people who went on a special journey to the cliff. That’s one of the major shortcomings of the X-ray analysis.

“If someone sends me an artifact, I can determine the origin of it with a good degree of confidence,” Dr. Shackley said. “But determining how it got there is the kicker.”

In the early 1890s, excavators digging in Mound 25 at the Hopewell location near Chillicothe, Ohio, found an altar with more than 100 burned and broken obsidian spear points, also known as bifaces. One point was more than 17 inches long and 6 inches wide and believed to have been designed for ceremonial purposes. About three-fourths the obsidian at Hopewell has been traced back to Obsidian Cliff using the X-ray tech.

“The largest of these bifaces are master works, really remarkable,” said Timothy D. Everhart, a museum curator and archaeologist at the Hopewell park.

The allure of Obsidian Cliff’s stone glass can be seen as well as felt in its efficient use as a sharp weapon. In a recent paper, researchers outlined its noteworthy elements — abundance, access, aesthetics and quality.

There is so much that the obsidian here could fill 3,000 stadiums the size of the Rose Bowl in California, Dr. MacDonald said.