[3] During this normally slow process, the retreating falls intersected with an ancient pre-glacial river bed inside Saint David's Buried Gorge.

During the retreat of ice from the Wisconsin glaciation of the Last Glacial Period, the gorge was filled with loose sediment and rock.

When the falls intersected with this buried gorge, the river quickly washed away the filled-in silt and rocks.

Further erosion of the harder rock has resulted in a rounded basin that extends just to the side of the actual river's course.

When more water from the river is diverted to the surrounding hydroelectric power plants, however, the whirlpool direction often reverses.