The Harper Humanities Garden was the site of an archeological dig this spring. Larry Conyers, an associate professor in DU’s Anthropology Department, led students in using ground-penetrating radar (GPR) along with old-fashioned shovels to examine the site.
Conyers realized the garden behind the Mary Reed Building held interest 12 years ago when he had a five-foot trench dug to show students layers of soil. Two feet down, a layer of charcoal and pieces of pottery were exposed.
Before DU began construction in 1890, the campus was home to Rufus Clark’s 150-acre potato farm. The pottery and charcoal, Conyers hypothesized, could indicate a trash pile from the old homestead.
Using GPR technology
This spring, Conyers’ Field Methods in Archeology and a special course in GPR took a closer look. First, students mapped out a grid. Then, they pulled an antenna that transmits electromagnetic pulses into the ground.
When radar energy goes through materials in the earth and encounters materials of different composition, its velocity changes. A second antenna records reflections and a computer tracks their location and intensity.
Thousands of reflections are processed in three-dimensions, their shape and intensity indicating soil disturbances or where something is buried. Six of those spots were excavated.
“Our initial hypotheses were for the most part wrong,” Conyers says.
Horizontal layers were presumed to be floors but turned out to be the remains of an asphalt road and adjoining sidewalk.
After analyzing the GPR data, teams of three students each excavated the locations where radar had encountered what appeared to be different materials. They found broken pottery, square nails and scorched brick. They also located numerous charcoal layers — indicating at least one exceptionally intense fire, as glass had been completely melted and re-solidified.
Freshman anthropology and theater major Sarah Johnson analyzed the radar data and excavated the site.
“We found a couple of different areas with higher amplitude reflections,” Johnson says. “That means there is something different in the soil that is hard and dense. We assumed it was a floor or foundation because it was a square, about two meters in diameter.”
Where did the road, sidewalk and curb lead? Was there a fire there? Or were charred remains piled there from elsewhere?
“From 1910–40, as far as we can tell, there was nothing there,” says University Archivist Steve Fisher. “The earliest aerials we have from the 1920s don’t show anything. It’s a mystery.”
Assistant Anthropology Professor Bonnie Clark dated the broken glassware, pottery chards and nails. Yellow glass indicated the presence of arsenic, which was common in fine tableware around 1900.
Decorations atop the ceramic glazed pieces were produced after 1900 and square nails were manufactured from 1880–1920, Clark says.
“We don’t understand this intense burning event,” Conyers says. “We never found the foundation of a building, but we found the remains of what appears to be a burned house.”
Anyone who has information about the site may contact Conyers at email@example.com or 303-871-2684.