The Mortlach Phase continued:

The pottery assemblages are highly diverse but quite distinctive in comparison to surrounding ceramic styles. Perhaps most identifiable are the thin-walled vessels with complex dentate-stamped decoration on wedge-shaped rims. Dentate stamping is a term used to describe impressions formed by pressing a thin notched tool rather like a comb into still malleable clay surfaces. While a variety of surface finishes are present in Mortlach ceramic assemblages, the check-stamped exterior surfaces are the most readily identified. Check-stamping patterns are produced by use of a paddle that has been cross cut into square or diamond shapes.

The arrowheads associated with the Mortlach Phase are also distinctively styled Plains Side Notch points many of which are formed on Knife River Flint from northern North Dakota and fused shale from the Estevan and Big Muddy areas of southernmost Saskatchewan.

It has been suggested that the Mortlach Phase is the precontact material culture manifestation of Assiniboine groups. If the correlation of Mortlach with Assiniboine peoples is correct, it is most likely that Mortlach pottery in Alberta represents short-term terminal Late Precontact/Protohistoric intrusions for trading or raiding by Assiniboines into largely Blackfoot
territory.