[3] The centerpiece of the 778-acre (3.15 km2)[4] park is a 400-foot-deep (120 m) narrow gorge cut through rock by Glen Creek, a stream that was left hanging when glaciers of the Ice age deepened the Seneca valley, increasing the tributary stream gradient to create rapids and waterfalls wherever there were layers of hard rock.

Around two million years ago the first of many continental glaciers of the Laurentide Ice Sheet moved southward from the Hudson Bay area, initiating the Pleistocene glaciation.

Glacial debris, possibly including terminal moraines, left behind by the receding ice acted as dams, allowing lakes to form.

The steep drop of Glen Creek into Seneca Valley created a powerful torrent that eroded the underlying rock, cutting further and further back towards the stream's headwaters.

Watkins Glen State Park now encompasses nineteen waterfalls spaced along a trail roughly two miles (3.2 km) long.