[2] The Ottawa-Bonnechere Graben measures about 700 km (435 mi), running from the Montreal area on the east to near Sudbury and Lake Nipissing on the west.

[7] These features are subterranean geological structures formed by the violent, supersonic eruption of deep-origin volcanoes.

[citation needed] Minor but significant igneous activity occurred during the Mesozoic era, including kimberlite emplacement during the Jurassic period, and the development of alkalic intrusions along the Ottawa-Bonnechere Graben and elsewhere in Ontario.

These are thought to have formed as a result of the North American plate sliding westward over a long-lived center of upwelling magma called the New England hotspot,[8] and is the eroded remnants of intrusive stocks.

Along the northern side of the Ottawa-Bonnechere Graben lies a dramatic escarpment that forms the southern edge of the Gatineau Hills.

It is calculated that the impact released energy equaling 250 megatons of TNT and occurred when this area was probably covered by a shallow sea.

The depressions formed by the graben across the rugged Canadian Shield were a spillway for the Great Lakes after the last ice age.

[13] [14] The valley of the Ottawa and Montreal Rivers and Lake Timiskaming was also part of a branch route to James Bay in the days of the fur brigades.

[16] After the arrival of European settlers in North America, the Mattawa River was an important transportation corridor for native peoples of the region and formed part of the water route leading west to Lake Superior in the days of the fur trade.