These strata lie unconformably and sharply on the Precambrian Grenville basement, however, this basal contact is rarely exposed.

The Shadow Lake Formation is poorly exposed, typically occurring in small isolated outcrops along a low escarpment capped by the more resistant carbonate beds of the overlying Gull River Formation.

[1] The Shadow Lake Formation consists of non-fossiliferous, red, maroon and green, poorly sorted, argillaceous, arkosic sandstones and conglomerates, arenaceous (sandy) siliciclastic mudstones (shales) and siltstones, and minor argillaceous dolomite and limestones.

[1] The Shadow Lake Formation, originally named by Okulitch (1939) based on outcrops north of Coboconk, was redefined by Liberty (1969).

The upper contact of the Shadow Lake Formation is placed where its mainly siliciclastic sediments give way to mainly carbonate sediments (typically argillaceous dolomites) of the lower Gull River Formation.