The Pleistocene deposits are divided into the following stratigraphic units, in order of decreasing age: Saskatchewan gravels and sands, Wolf Island sediments, Elkwater drift, Cypress Hills loess, Wild Horse drift, Pakowki drift, Manyberries volcanic ash, Etzikom drift, and Oldman drift. The drift sheets are morphostratigraphic units; each one was deposited at the time of a significant glacial advance. Correlation of subsurface tills with these surface drift sheets is presently not possible because of the sparse number of C-14 dates and lack of recognition of critical sedimentary parameters.

The Saskatchewan gravels and sands are fluvial deposits that floor the major preglacial valleys. They lie unconformably upon Upper Cretaceous rocks and are composed dominantly of quartzite pebbles. Wolf Island sediments consist of sands, silts, and clays that accumlulated in elongate proglacial lakes which formed along the preglacial valleys as a result of damming downstream by Laurentide ice. All the drift sheets were deposited by Laurentide glaciers.

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Ages from late Tertiary to middle Pleistocene have been suggested for the Saskatchewan gravels and sands by past workers. The presence of frost action structures and remains of Mammuthus primigenius definitely indicate a Pleistocene age for the upper part; remains of Equus sp., somewhat smaller than Equus caballus, have also been recovered and a C-14 date of greater than 36,600 years was obtained on wood collected from the upper part of these gravels and sands. The Elkwater drift has suffered considerable mass-wasting and undrained depressions are few; its age is regarded as post-Sangamon, pre-"classical" Wisconsin. The fresh-looking morainal topography and lack of drainage integration of the Wild Horse and younger drifts suggest that none of these drift sheets is older than the "classical" Wisconsin. The minimum age of the Oldman drift is 10,500±200 years.

No severely weathered horizons have been observed between tills exposed along valley walls. However, two subsurface tills near Lethbridge are greater than 54,500 years old indicating that tills of early Wisconsin age or older are present in southern Alberta.

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