Sedimentology of Upper Cretaceous and Tertiary siliciclastics and coals in the Raton Basin, New Mexico and Colorado
— Romeo M. Flores

The Raton Basin was a major site of siliciclastic and coal accumulation in coastal and alluvial plains from the Late Cretaceous to early Tertiary. The coastal plain was developed along the western margin of the Cretaceous epeiric seaway and consisted of barred and non-barred siliciclastic coastlines. The barred coastline included coastal-attached beach ridges, estuarine-fluvial channels and a back-beach marsh-swamp complex. The barred coastline was attached laterally to the non-barred coastline, which was constructed by delta systems that were fluvially dominated but minimally affected by wave and tidal processes. The Upper Cretaceous Pierre Shale, Trinidad Sandstone and Vermejo Formation were deposited in these siliciclastic coastal environments.

During the Laramide orogeny, the coastal plain was transformed into an alluvial plain of through-flow fluvial systems that drained on a foreland basin. The alluvial plain was built by braided, meandering and anastomosed streams. The braided streams generated sand-dominated facies, and the meandering and anastomosed streams Produced fine-detritus-dominated facies. Coals are preferentially associated with the fine-detritus-dominated facies in which autocyclic processes of the fluvial systems, increased basin subsidence concurrent with diminished uplift of the source area and climate favored organic accumulation. The Maestrichtian and Paleocene Raton and Poison Canyon formations were deposited in these siliciclastic alluvial environments.