Stratigraphy, facies and paleotectonics of the Mississippian system, Sangre de Cristo Mountains, New Mexico and Colorado and adjacent areas
— Augustus K. Armstrong and B. L. Mamet

Lowermost Mississippian deposits of the Sangre de Cristo Mountains in north-central New Mexico comprise the upper Osagean (zone 9) Espiritu Santo Formation. These sedimentary rocks rest unconformably on Proterozoic metamorphic and igneous rocks. In the Sangre de Cristo Mountains of south-central Colorado, the Mississippian Leadville Limestone overlies rocks of Ordovician or Late Devonian age. Mississippian carbonate sediments were deposited during a regional marine transgression across northern New Mexico and southern Colorado. This transgression and preceding Mississippian regression are events related to the Antler orogeny. The Osagean (Early Mississippian) marine transgression advanced from the south and west over a nearly peneplained terrane. Nearshore sediments include supratidal and intertidal lime mudstones, anhydrites, gypsum, dolomites, quartz sandstones and shales.

The Osagean sediments, in more open marine environments, were calcareous sand shoals composed of pellets, bioclasts of crinoids, brachiopods, bryozoans and ooids and oolites. The end of Osagean time was marked by a regional marine regression and erosion of Osagean carbonate rocks.

A regional marine transgression of Meramecian age is documented from the upper part of the Leadville Limestone in the subsurface data of southeastern Utah and in the western part of the San Juan Basin, in outcrops of the Tererro Formation in the Nacimiento and San Pedro Mountains and in the Sangre de Cristo Mountains of north-central New Mexico. Evidence of this transgression is also present in the upper part of the Leadville Limestone in the Sangre de Cristo Mountains of Colorado, in the Leadville Limestone of the Front Range of Colorado and the subsurface of eastern Colorado. These carbonate rocks from southern Colorado are composed of dolomites, lime mudstones, ooid-oolites, crinoids, foraminiferans, algae, brachiopods and pellets. Early Chesterian age (zone I6i) carbonate sediments are known only in the Cowles Member of the Tererro Formation in the Sangre de Cristo Mountains of New Mexico. They are arenaceous-peloid-crinoid-bryzoan wackestones to packstones.

In the Late Mississippian and Early Pennsylvanian, southern Colorado and northern New Mexico were differentially uplifted during the Ouachita orogeny, and large areas of Mississippian rocks were partially or completely removed. The remaining carbonates were subjected to solution and karstification and the development of a thick regolith. In the San Pedro, Nacimiento and Sandia Mountains the Mississippian carbonate rocks of the Arroyo Penasco Group are unconformably overlain by the continental red beds of the Log Springs Formation (Chesterian). In the San Juan Mountains, Sangre de Cristo Mountains and Mosquito Range Mountains of Colorado, this regolith on top of Mississippian rocks was reworked and redeposited by the transgressive Pennsylvanian sea and formed the Molas Formation. Mississippian sedimentary rocks are disconformably overlain by Pennsylvanian sedimentary deposits.