These beds have the same bright red color as those of the Grinnell.
However, because they are the youngest rocks of the Belt series they
outcrop only on a few mountaintops, and inasmuch as these are mainly in
the northwest part of the park, comparatively few people have noticed
this formation. Visitors to Cameron Lake in Waterton Lakes National Park
can see it in the red north wall of Mount Custer. The mountains around
colorful Boulder Pass and Hole-in-the-Wall Basin are likewise composed
of it.
Within the rocks of this formation there is a great abundance of small
cubes believed to be casts of salt crystals which formed when the
sediments were accumulating. Their presence indicates an arid climate
and intensive evaporation of the sea, similar to the condition at Great
Salt Lake today.