Archaeologist Stephen Aaberg was surprised with the results of radiocarbon dating tests just completed on samples taken from trenches dug in Alkali Creek (Montana, USA) last summer. The sample that dated to most recent times - charcoal picked from a hearth uncovered 6 to 10 inches below the grassy surface - was determined to be 1,050 years old. The oldest, a bison foot bone found near stone artifacts, was dated at 5,300 years old.
     About 18 inches below the 5,300-year level, archaeologists working for Aaberg's company found a single piece of charcoal. Aaberg isn't sure what to make of it but believes it could be 7,000 to 8,000 years old. Also found at that level was a fragment of a long, narrow projectile point characteristic of that ancient period. "We were surprised by the dates, but not so surprised that we just couldn't accept the data," Aaberg said.
     Aaberg was hired by the state Department of Transportation to document the area in preparation for rebuilding Airport Road. In 2005, he walked both sides of the portion of Alkali Creek Road that would be included in the project, looking for signs of early human occupation. He found enough on the surface to warrant digging meter-square test pits. "We came right down on an old hearth," he said. "The site ended up being really substantially large." Aaberg's report found that the road project would have a significant impact on the archaeological site, which prompted the excavations of 2007 to document the archaeology before the bulldozers started moving earth.
     Crews worked clearing 10 centimeters of soil at a time at likely spots within the perimeter of the site. They found cutting tools, stone knives, broken projectile points, animal bone and "pebble cores," the characteristically scarred rock left over after flakes were chipped off to make tools. The first major feature was the hearth that proved to be 1,050 years old. Its builders had dug a little pit, and inside were fire-cracked rock and an abundance of charcoal. About 4 feet below the first pit, archaeologists digging a trench with a backhoe found a second hearth of almost identical construction. The second hearth was dated to 2,600 years ago. Evidence suggests that these hearths probably were used to heat rocks that would be dropped into separate cooking pits filled with water for boiling food, Aaberg explained.
     About 90 yards from the pit used to heat rock, archaeologists found what they believe is a stone boiling pit where food would have been cooked. They found the bones of grouse-sized birds, deer and antelope as well as bison. There weren't enough bison bones to indicate that large numbers of animals were processed there at one time. Researchers did find some obsidian that may have been brought from the area of Yellowstone National Park, but Aaberg suggests that it may have been acquired through trade rather than travel.
     The occupation site at Alkali Creek was likely a seasonal camp, although it's hard to tell what season. The fact that most tools were made from local rock may indicate that people camped there during the winter, when they were less mobile, Aaberg speculated. "What we can say is that particularly in the period beginning about 5,300 to 5,200 years ago, there are archaeological sites and artifacts all over Montana, especially east of the Divide," he said. "My guess is that there was a heck of a population. The game populations were high enough to support a pretty large human population." These people probably lived in animal hide tepees and hunted efficiently with the same type of spear throwers for thousands of years.
     The Alkali Creek site presented archaeologists with a rare treasure - up to 15 acres of pristine ground, rich in artifacts, in the middle of a metropolitan area that has never been touched by a plow or residential or commercial development. Other cities have turned such resources into parks and cultural attractions, Aaberg said.

Sources: Billings Gazette, Helenair.com (22 December 2007)