At the time this was an important part in making gunpowder and would be for nearly five years a primary source of saltpeter for the Ontario powder works in 1852.

Caribou Island was considered for an emergency landing airport (YCI) during World War II but it was never built because of the proximity of the twin cities of Sault Ste.

[1][3] In addition, exposures of gently dipping, friable Jacobsville Sandstone, have been reported from Caribou Island.

A shallow reef 2.5 miles (4.0 km) to the southwest of Caribou Island Lighthouse lies only 11 feet (3.4 m) below the lake's surface.

These tunnel valleys were excavated by subglacial meltwater at the base of the Laurentide Ice Sheet along pre-existing fractures and joints that exist within the bedrock floor of Lake Superior.

[3][8][9] Samples dredged from a shoal northwest of Caribou Island and close to one of these valleys resemble Jacobsville Sandstone.

The lateral continuity and consistent and parallel direction of the tunnel valleys indicated that they are carved from friable sandstones that underlies the floor of most of eastern Lake Superior.