Molas Formation
The Molas Formation is a geologic formation that is found in the Four Corners region of the United States. Its age is poorly constrained but is thought to be Namurian.
Description
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 and may correlate with the Log Springs Formation in the Jemez Mountains of New Mexico. It has also been interpreted as a loess trapped on the karst surface of the underlying limestone. 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.
The formation is exposed in the San Juan Mountains, the Sangre de Cristo Mountains, the Mosquito Range, the Sawatch Range, and at Glenwood Springs, Colorado. It exists in the subsurface throughout the San Juan basin.