The northern edge of Phanerozoic platformal rocks of the Western Canada Sedimentary Basin overlies the Flin Flon Belt (Trans-Hudson Orogen) in Manitoba and Saskatchewan. A program of regional mapping of the Phanerozoic-covered basement has been undertaken, involving the integration of high-resolution aeromagnetic and gravity data with extensive drill core information. Several major domains are recognized in the buried basement, each with a distinct lithotectonic character and potential field anomaly pattern. Three lithotectonic domains in the buried basement (Clearwater, Athapapuskow, and Amisk Lake domains) are characterized by northerly-trending positive gravity and aeromagnetic anomalies and correlate with the 1.92–1.83 Ga volcanic and plutonic rocks of the exposed Flin Flon Belt (Amisk collage and Snow Lake assemblage). An upper amphibolite grade orthogneiss complex (Namew Gneiss Complex), containing calc-alkaline intrusive rocks ranging in age from 1.88 to 1.83 Ga and screens derived from the older volcano-sedimentary rocks, is interpreted as the middle crust of a 1.88–1.84 Ga arc exposed in the Flin Flon Belt. Discordant intrusive complexes, such as the 1.830 Ga Cormorant Batholith, are centred on magnetic–gravity lows and truncate the structural trend of adjacent lithotectonic domains. Correlation of Flin Flon Belt geology with that beneath the Phanerozoic cover shows that its constituent lithotectonic elements have north–south strikes of up to 150 km, and form a predominantly east-dipping crustal section, consistent with Lithoprobe seismic reflection profiles.