Geologic map of Van Bremmer Park Quadrangle, Colfax County, New Mexico

The Raton basin is a large asymmetric syncline (2500 mi2 area) that extends from Huerfano Park, Colorado to Cimarron, New Mexico. As used here, the basin is defined by the limits of the outcrop of the Trinidad Sandstone. The Cretaceous and Tertiary rocks are sharply flexed to form hogbacks along the western margin of the basin on the east flank of the Sangre de Cristo Mountains. These rocks assume more gentle dips along the other margins of the Raton basin and are highly dissected. The Late Cretaceous in the Raton basin was a period of emergence of land and retreat of the Cretaceous epeiric sea. The coastline advanced eastward across New Mexico, as broad prograding deltaic and barrier coastal plains were formed seaward of aggrading fluvial systems. This map depicts the stratigraphic context and areal extent of uppermost Cretaceous and Paleocene rocks in the Raton basin including the marine Pierre Shale, marginal-marine Trinidad Sandstone, non-marine coal-bearing Vermejo Formation, non-marine coal-bearing Raton Formation and non-marine, non-coal-bearing Poison Canyon Formation.