Named after Tunnel Mountain near Banff, it was deposited during the Early Pennsylvanian sub-period of the Carboniferous period.

[2][3] The Tunnel Mountain Formation consists of quartzose sandstone, interbedded with lesser amounts of dolomite, dolomitic sandstone in the lower part, and minor beds of quartzite in the upper part.

[3][4] The dolomite beds of the Tunnel Mountain sequence include scattered brachiopods and foraminifera.

[2][3] The Tunnel Mountain Formation is present in the front ranges of the Canadian Rockies of western Alberta, and reaches a maximum thickness of about 200 metres (600 ft).

In areas where the Kananaskis is not present, it is unconformably overlain by the Permian Ishbel Group.