The Molas Formation is a sequence of continental
red beds. It is divided into three
members. The lowermost Coalbank Hill Member is up to of purplish-red to reddish-brown
siltstone and
conglomerate. This is overlain by an informal middle member, consisting of
mudrock,
sandstone, and conglomerate, that is typically around . The upper member is typically around that includes maroon to light gray sandstone. The upper member grades into the overlying
Pinkerton Trail Formation. The Coalbank Hill Member may be a
terra rossa (a residual soil formed by
weathering of the underlying
Leadville Limestone) and may
correlate with the
Log Springs Formation in the
Jemez Mountains of
New Mexico. The middle member and much of the upper member were deposited in a river system that reworked the Coalbank Hill Member sediments, while the upper member includes some marine beds. The boundary between the middle and upper members is set where
kaolinite clay becomes more abundant than
illite clay. ==Fossils==