By David Mather
Three archaeologists uncover their excavation trench, carefully pulling up sheets of plywood. My breath quickens with the first glimpse underneath.
Dubbed the "Ring of Fire" in the local press, this circle of stones is ancient, its purpose shrouded in mystery. It is a remarkable discovery, but just one of several in this grassy field.
I'm in southern Minnesota, alongside state parks archaeologists Dave Radford, Doug George, and LeRoy Gonsior on a dig in Fort Ridgely State Park. We turn around to see another excavation. This pit reveals remnants of a field kitchen that fed Col. Henry Sibley's troops in 1862.
Sibley led the hastily assembled Minnesota troops against Dakota warriors, who were trying to reclaim their ancestral homeland in the face of starvation and broken treaties. While Union and Confederate armies clashed in the eastern states, the five-week U.S.–Dakota War was Minnesota's own Civil War, leaving a painful legacy that still haunts Minnesotans today.
Although the earth here is heavy with cannonball shrapnel from the start of the war, we are surrounded by sites of American Indian villages stretching far back into the early reaches of Minnesota's human history. These archaeological layers are physically close but scattered across millennia, from the end of the last Ice Age to the U.S.–Dakota War. All the artifacts are buried in deep, rich prairie soils. They share this ridge overlooking the wide Minnesota River valley, where they were recently discovered because of golf.
In 2005 the park's golf course—originally built in 1926—was due for renovation. Before such construction work can commence in state parks, archaeological investigations are required to ensure that important historical sites won't be disturbed. Radford, George, and Gonsior knew that the ruins here mark the scene of a legendary battle. As they sunk their shovels into the soil, they found that the full history of this place is a greater story, with origins far deeper in time.
Snapshots of History
The stone circle that the archaeologists found appears deceptively simple at first. It measures nearly 5 feet across. Individually, the stones are rather plain, but they were placed long ago in this pattern, a near perfect circle with a small opening to the east. Many of the stones are big, nearly the size of volleyballs. The archaeologists point out their unnatural color and telltale cracks: These stones were heated by fire at some time in the past, until they were glowing hot.
Hot rocks were used for cooking and heating, but archaeologists usually find only scattered pieces. This circle is not only large, but also the rocks are still mostly intact. If the source of heat was a fire within the ring, it must have been huge and maintained for a long time. Or, perhaps it was used repeatedly. But there is no charcoal in the circle, compounding the mystery.
The circle seems too big for a cooking fire. Perhaps it was a place for community gatherings or rituals. Perhaps a larger fire was a signal, big enough to reach across the wide valley. The state parks archaeologists hesitate to offer interpretations without more evidence, but their individual personalities come out as they discuss possible dates.
Radford cautiously suggests that it may be 3,000 years old or more, because it was found at a lower depth than pottery and other artifacts from the Woodland period, which began about 200 B.C.
George carries this implication further, suggesting that it is at least as old as the Archaic period, a long span from about 7,500 to 2,200 years ago. Like Radford, he believes that charcoal once present within the circle has leached away due to its great age. Both point out that the stones are deep within the soil profile.
Gonsior listens to their explanations and then states without hesitation, "It's Paleo," archaeological shorthand for the Paleoindian period. This is the time of the first people entering North America, at the end of the Ice Age. In southern Minnesota, this period lasted from at least 12,000 until about 7,500 years ago. During this time, Glacial River Warren carved out the wide gorge of the Minnesota River and then reoccupied it at least once more, as the drainage of Glacial Lake Agassiz shifted. It is possible that the water-filled valley was an impassible barrier at times.
The archaeologists debate the stone circle's age because they found no diagnostic artifacts—no finished pieces such as points or pottery that indicate a known time period. And without charcoal, they cannot run radiocarbon dates. Gonsior argues for a Paleoindian date partly because Paleoindian spearpoints have been found elsewhere in the park and along this part of the river valley.
Back in 2006, the three archaeologists were working outward from the chipping debris when they found the stone circle. These chips, "flakes" to archaeologists, were the byproduct of making stone tools. The chips surrounded two boulders, which likely provided a natural spot for flint knappers to sit and visit as they worked. Radford points out that the vantage across the river valley would have made this a perfect spot for a hunting camp.
The excavation trenches slice the natural contours of the earth at sharp right angles. The walls are straight, and the floors flat. The archaeologists cut the turf by hand with flat shovels. They skimmed off thin slices of soil and placed them into a shaker screen. Throughout their dig, expert eyes scanned the freshly cut surfaces for artifacts or colors in the soil.
From the screen, they picked through pebbles, roots, worms, and grubs. They placed artifacts in bags labeled with the site name and number, excavation unit, level below ground, excavators' initials, and date.
Deep in the trench, the shovel suddenly clinked on a buried stone, then another, and another. The archaeologists switched to small hand tools—flat Marshalltown trowels, whisk brooms, brushes, and picks. Careful work slowly, achingly revealed an arc of stones and eventually the whole circle. Patience is more than a virtue in archaeology; it is a rule. And this time patience paid off.
The crew dug the trench in a series of levels. At each 5-centimeter interval, they scraped clean, mapped, and photographed the soil. With each shot, they included a written description and an arrow pointing north. They bagged some of the soil from inside the circle, in hopes that future laboratory analysis might reveal more about its age or function.
Through their investigation, the archaeologists recognized that this circle just wasn't something that could be removed. Without their ancient position in the soil, the individual stones would lose their identity. Archaeology is about finding information, rather than just artifacts, and often the best outcome for historical sites is simply to put them back the way they were in the first place. To preserve the integrity of the circle, the stones were left in place and reburied.
The excavation trench with the stone circle was one of many that archaeologists dug within the proposed golf course design. Like the circle, areas with significant finds were left intact. The architect adjusted the layout of fairways, tees and greens, and the irrigation pond to preserve the park's history.
The history of the Minnesota River offers two contrasting scenes for the creation of the stone circle. The present-day river is a classic example of an underfit stream, a toddler dressed in its parents' clothes. About 11,500 years ago, a torrent of glacial meltwater raged loose from Glacial Lake Agassiz at the southern end of today's Red River valley. The torrent cut a vast trench that became today's Minnesota River valley. If the stone circle was made then, this might have been the scene:
Paleoindian hunters see the glacial river filling the expansive valley, a mile wide at this location. Woolly mammoths, giant bison, and other now-extinct Ice Age animals roam the uplands. The air feels cold and damp. People gather here at the boulders and sharpen their weapons, surrounded by a spruce and pine forest. Their spears are tipped with long, finely flaked stone points, ready for the hunters to hurl with great force and accuracy using a hand-held spear thrower. The bonfire rages nearby, calling their clan to this place.
If the stones were laid 7,000 years ago, during the Archaic period, the scene might have looked different:
Prairie crowns the uplands, opening sight lines in every direction. The river has shrunk to its present size, far below in the valley. Even in this dry, warm climate, the wet floodplain provides wood and shelter from prairie fires. Torches in hand, hunters wait at the boulders, some using the time to sharpen their weapons. A runner brings word of a bison herd moving along the valley edge below, and the hunters light the fire in the circle.
Of course, we have no proof that the stone circle was a beacon. I imagine that function because a fire big enough to scorch these stones would have been visible at a great distance. The circle and the toolmakers' station are near the valley edge, conspicuous to others within and across the wide valley. Such pondering, made possible through these "pinpoints in time," as George calls the stone circle, is one of the most compelling aspects of archaeology. The stone circle has one ancient truth, all but unknowable to us today, but it offers an infinite number of stories. We each create them as we puzzle through the evidence in our own way.
Archaeology, more like a CSI television show than an Indiana Jones movie, begins with some knowledge of previous events. Investigators systematically search for evidence to fill in the story. Important clues include artifacts in the ground, the lay of the land, patterns of vegetation, and unusual layers or colors in the soil. Everything is recorded. An undocumented artifact has lost most of its historical and scientific value. If the context is gone, there's no story to reconstruct.
Given the challenge of guiding a golf-course development in this important area, the archaeologists started with the most accessible historical layer, the ruins of Fort Ridgely and accounts of the battle. But George knew that the visible ruins were only part of the fort, and that the battlefield was larger still. In the 1930s, archaeologist G. Hubert Smith uncovered only some of the fort's foundations. The commissary, the only standing building today, was restored at that time.
With no stockade to protect the soldiers, and two ravines offering cover for the attackers, Fort Ridgely was not well situated for defense in 1862. It was particularly vulnerable in the first days of the war: The fort's commander and many of the seasoned troops had been killed two days before at Redwood Ferry, near present-day Morton. Only 22 soldiers remained at the fort, serving under the command of a junior officer with the mumps. Refugees were streaming in from Lower Sioux Agency.
Now George walks me through the events of those hot August days and the archaeological finds that have redrawn the battlefield. As we stand in the fort's ruins, he points to the nearby head of the eastern ravine, and the desperate situation of the fort's defenders comes into focus. Dakota forces came into view from the ravine, and the soldiers met them with artillery fire. But the first barrage completely overshot the ravine. The cannonballs were set to explode on two-second fuses (creating a spray of shrapnel for the archaeologists to find 144 years later). The gunners cut the fuses back, and back again to a half-second, and eventually repelled the first attack.
George points away from the fort to the north, to a higher point where Little Crow oversaw the battle, and then west, to the other ravine and the former location of the stable. These and other sight lines are important features of the battlefield. Based on George's historical reconstruction, the golf-course designers protected the sight lines by adjusting the height and placement of tees and greens.
Walking the battlefield today, we see no hint of the wooden stable that housed the troop's horses, exposed to attack near the western ravine. Once Dakota forces occupied the stable, the defenders in the heart of the fort focused the big guns to destroy the building. It burned, and over years the traces disappeared into the earth.
Since the stable played such a prominent role in the battle, finding its location was key to understanding the extent of the battlefield. George first narrowed down a search area. A series of small, round shovel tests turned up old nails—a promising clue. But the stable was too large to define by digging. This task called for technology, so a magnetometer was brought in to trace the full footprint of the building. An archaeologist carried the long magnetic pole back and forth across the area, measuring the differing magnetic resistance in the ground. A ghost image of the stable's outline took form on a laptop computer nearby.
When Smith was digging on the old fort grounds in the 1930s, he was surprised to find ancient pottery at the end of one building, at a lower level than the other debris. The pottery was a style that archaeologists now call Oneota, used by American Indian farmers along the Minnesota River (and elsewhere) from about 1000 to 1650 A.D.
Gonsior shows me a handful of tiny triangular arrowheads from the same period. They are barely 1 centimeter long, but they once tipped arrows so finely made that they were used to hunt bison. In addition to their valuable meat and hides, the bison provided shoulder blades for hoes that Oneota farmers used to till the rich floodplain soil.
Archaeology provides one way of connecting to the past, a complement to oral traditions and written records. It brings new insights to the tragic war of 1862, while also reminding us that it was just one chapter. A far longer, older story remains to be told. The artifacts of the Oneota farmers and hunters can show us the Minnesota River valley in its natural state and offer us a bridge into the distant past.
Far back there, deep in time, the stone circle was created. It still watches over the valley, an ancient presence near the third green.