He hit something solid around two feet down and stabbed a few more times to trace the object.
It's rectangular, he said - large enough to be a cemetery vault for a child.
Or, maybe just a random slab of concrete or piece of pipe.
"That's why we are here - to find out," said Moates, regional director for the Florida Public Archaeology Network.
The search for Zion Cemetery has begun.
A burial ground for as many as 800 African-Americans during the early 1900s, Zion had been forgotten for decades until the Tampa Bay Times raised questions with a special report in June about whether the bodies were ever moved or whether they remain on land that's now occupied by apartments and warehouses.
To help find an answer, the Tampa Housing Authority - owner of the apartments - hired private archaeological assessment firm Cardno to inspect its portion of the 2 1/2 acres that once was Zion Cemetery. Moates and his group are helping in the search of the property, along the 3700 block of North Florida Avenue.
The cost of the survey is still being determined, said Leroy Moore, chief operating officer of the housing authority. An archeological assessment would have been necessary even if the cemetery hadn't been rediscovered, Moore said, because the authority plans to develop the property in the future.
Five of the 67 apartment buildings that make up the authority's Robles Park Village stand on land that once was the cemetery. In field work Monday (Aug. 5), archaeologists used GPS data to create a digital grid map of land along Moore and Kentucky courts.
They went beyond the cemetery land, too, in part because the old maps they're relying on might not align exactly with the cemetery land, said Paul Jones, project manager for Cardno. Another reason: It was common for families during the early 1900s to bury loved ones on their own, just outside a cemetery, to save the cost of buying a plot.
Next week, the team will start using ground penetrating radar to search each section outlined on the new digital map.
They brought along the radar equipment this week, mounted on a wheeled cart, but just to get a feel for the terrain. They also checked the depth of buildings' foundations and utilities.
What they've found so far indicates that apartment foundations and utility trenches are so shallow they might have been built on top of graves, said Eric Prendergast, Cardno's principal project investigator.
How deep graves might lie remains unknown.
"I think six feet is a wise figure but there isn't a typical" depth, said Moates, with the archeology network.
One example: In 1951, three caskets were unearthed just 15 inches under the ground during the construction of Robles Park. Why the discovery didn't raise red flags about the larger cemetery property remains unclear. Housing authority minutes from that time mention no effort to search for more graves.
If underground anomalies that might signal burial plots are discovered, the archaeologists will later take their search a step further. They'll dig into the earth, just beyond the anomalies to avoid disturbing them.
Their tools don't enable them to search beneath buildings so the investigation is limited to green space, sidewalks and parking lots.
They'll first train their ground penetrating radar on land near the corner of Moore and Virginia avenues where the caskets were found in 1951 and the location, according to old maps, of a potter's field for indigent burials.
"It is less likely that the potter's field was moved, as opposed to officially platted grave plots," Prendergast said.
Eunive Massey, 96, grew up next to Zion and recalled to the Times seeing bodies exhumed around 1933 in a disorganized process that left human remains exposed.
Massey's description leads the archeologists to believe that bodies have indeed been left behind, especially on the edges of the cemetery.
"They probably went to the center, got everything they could and hauled it away," said Jones with Cardno.
A map of Zion Cemetery filed with Hillsborough County in 1901 shows boundaries extending to Florida Avenue with room for some 800 graves.
In its research, the Times discovered death certificates for 382 people listing Zion Cemetery as the burial place. The June 23 report prompted cemetery historian Rey Reed to conduct his own research and he turned up 747 death certificates listing Zion.
Massey recalled that by the 1930s, a storefront had been built along Florida Avenue, with three homes behind it and the cemetery behind the homes. Walking the property where the homes once stood, the archaeologists came up several concrete blocks that appear to be pillars used to raise the homes off the ground.
It was here that Moates and his probe struck what might be a burial vault.
The team is eager to return for a deeper look.
If they find graves, the chances increase that there will be more on the adjoining cemetery land - the half owned by Tampa restaurateur Richard Gonzmart.
"We're watching to see what their investigation reveals," Gonzmart's attorney Jeffrey Shannon told the Times in an email. "At the same time, we're continuing our own research into title and other legal documents."
Information from: Tampa Bay Times (St. Petersburg, Fla.), http://www.tampabay.com.
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