Teams of archaeologists are working three “digs” in construction areas of Des Moines this week. Some of the objects they’re finding date back centuries, according to Patricia Ohlerking, the deputy state historical preservation officer of the State Historical Society of Iowa.The oldest site is associated with Oneota culture, Indians who lived here between the 11-hundreds and the 16-hundreds. Other finds date from the 1840s when the U-S military post called the “Fort Des Moines Number Two” was still in use.Ohlerking says the pottery shards and buttons come from waste sites. That’s right, the archaeologists are picking through preserved garbage dumps from the distant past. She says other areas being studied include the foundations of commercial and residential buildings from the core of the town of Fort Des Moines.Ohlerking says it’s still not known if the city will permanently change its plans for the new road and parking lot. If not, archaeologists may have to extract what they can from the sites before the ground is paved over.