Native American groups occupied the Irwin Site off and on starting at least 8200 years ago, making it one of the oldest sites in Pennsylvania. The occupants likely settled there to hunt, gather plant foods, and possibly to fish in the nearby river. Because of the rugged terrain in the Appalachian Plateau of northern Pennsylvania, fewer Native American sites exist and most are along streams.

The Irwin Site is stratified, or layered, with the oldest occupations at the bottom. As Lick Run flooded repeatedly over time, occupation surfaces were covered with silt and separated from later occupations.

Archaeologists divide prehistory into named period to better understand and describe their findings. The profile to the right shows the history of occupation in the flood deposits at the Irwin Site.

The Late Woodland Occupation

The Early Woodland Occupation

The Late Archaic/Transitional Occupation

The Early Archaic Occupation

After being excavated in 4-inch layers, soil is pushed through screens to recover artifacts

One of the excavation blocks after completion