These red beds consist of basal fluvial-lacustrine conglomerates, sandstones, and shales overlain by cyclic dolomite-siltstone layers, stromatolites and red mudstones, which represent a playa lake, sabkha, and mudflat environments; purple shales and siltstones interpreted as subaerial mudflat deposits; and an upper unit of cross-stratified sandstone beds, which are interpreted to be aeolian in origin.

[5][6] The Sibley Group unconformably overlies highly deformed and metamorphosed Archean turbiditic sandstones and metavolcanic and granitic rocks.

Outside of the rift basin and east and west of Lake Nipigon, the Sibley Group is absent and erosion resistant Archean rocks are either exposed at the surface or blanketed by Pleistocene glacial sediments.

[5][6][7] The Archean and Proterozoic strata are intruded by a number of mafic and ultramafic intrusions, which define the current outline of the Nipigon Embayment.

The Nipigon diabase sills give evidence of rift-related continental basaltic magmatism during the Midcontinent Rift System event, estimated at 1,109 Ma ago.

The mafic and ultramafic intrusions in and around the Nipigon Embayment have widely been interpreted to represent a failed arm of the Midcontinent Rift System, although the lack of dike intrusions, compared to the relative abundance of flat, saucer-shaped sills in the embayment, has led some researchers to question the dominant failed rift arm model.

Although economic deposits have yet to be found, 1.53 billion-year-old anorogenic granites within the Lake Nipigon area potentially contain yttrium, zirconium, rare-earth elements and tin mineralization.

The clastic sedimentary rocks of the Sibley Group, are host to unconformity-related uranium and red beds-type copper ore deposits.

[15] On 17 April 1744, the Jean Frédéric Phélypeaux, Count of Maurepas, Minister of the Marine, informed the Canadian officials that Jean de La Porte was to be given the "fur ferme" (i.e. the profits) of Lac Alemipigon from that year forward as a reward for his services in New France.

The Municipality of Greenstone (pop 5662) was incorporated in 2001 and includes Orient Bay, MacDiarmid, Beardmore, Nakina, Longlac, Caramat, Jellicoe and Geraldton.

This water was diverted to boost the Sir Adam Beck Hydroelectric Generating Stations at Niagara Falls.

The first nations CBC TV series Spirit Bay was filmed on the lake at the Biinjitiwaabik Zaaging Anishinaabek Reserve in the mid-1980s.

Another branch of the CNR touches the southeastern section of the lake at Orient Bay and Macdiarmid before heading inland to Beardmore.

[19] Ontario Parks has designated the area as the Lake Nipigon Basin Signature Site, because of its remarkable range of natural and recreational values.

The site includes many provincial parks, conservation reserves, and enhanced management areas around the lake and within its watershed.