Saint David's Buried Gorge is an ancient pre-glacial river bed that existed 22,800 years ago on the present-day

Niagara Peninsula The Niagara Peninsula is an area of land lying between the southwestern shore of Lake Ontario and the northeastern shore of Lake Erie, in Ontario, Canada. Technically an isthmus rather than a peninsula, it stretches from the Niagara River in the ...

. The ancient Saint David's River once flowed through this area prior to the advance of the

Wisconsin glaciation The Wisconsin Glacial Episode, also called the Wisconsin glaciation, was the most recent glacial period of the North American ice sheet complex. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cor ...

during the Last Glacial Period. When the glacier retreated 12,000 years ago, the gorge and river valley were filled in with glacial silt and rocks. Approximately 4,200 years ago, the

Niagara River The Niagara River () is a river that flows north from Lake Erie to Lake Ontario. It forms part of the border between the province of Ontario in Canada (on the west) and the state of New York (state), New York in the United States (on the east) ...

intersected the buried gorge in the course of

Niagara Falls Niagara Falls () is a group of three waterfalls at the southern end of Niagara Gorge, spanning the border between the province of Ontario in Canada and the state of New York in the United States. The largest of the three is Horseshoe Falls, ...

receding toward

Lake Erie Lake Erie ( "eerie") is the fourth largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has t ...

. When the river encountered the glacial silt that filled the gorge, the river rapidly changed course to fill the ancient gorge and wash out most of the silt. This led to the formation of the

Niagara Whirlpool The Niagara Whirlpool is a natural whirlpool within the Niagara River located along the Canada–U.S. border between New York and Ontario. The whirlpool is in the Niagara Gorge, downstream from Niagara Falls. The whirlpool's greatest depth i ...

. The Niagara River reclaimed the gorge and currently flows through part of the ancient gorge. The other part of the ancient gorge extends into

Lake Ontario Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north, west, and southwest by the Canadian province of Ontario, and on the south and east by the U.S. state of New York. The Canada–United States border sp ...

at a different point than the Niagara River. The gorge is estimated to be long, wide, and deep. In the 1950s,

Ontario Hydro Ontario Hydro, established in 1906 as the Hydro-Electric Power Commission of Ontario, was a publicly owned electricity utility in the Province of Ontario. It was formed to build transmission lines to supply municipal utilities with electricity ge ...

dug two tunnels from the upper Niagara River to supply water to the Sir Adam Beck Hydroelectric Plant. These tunnels had to surface when they encountered the St. David's Gorge, as the loose silt in it was unsuitable for tunneling. In 2013, an additional tunnel, the Niagara Tunnel Project, was completed. This tunnel was bored beneath the old gorge to avoid the unsuitable geology.

References

{{coord, 43.150, N, 79.098, W, display=title Former rivers Canyons and gorges of Ontario Glaciology of Canada