Nacimiento Formation Nacimiento Formation The Nacimiento Formation is a sedimentary rock formation found in the San Juan Basin of western New Mexico (United States) and named for the Nacimiento Mountains. It is a heterogeneous nonmarine formation composed of shale, siltstone, and sandstone, deposited in floodplain, fluvial and lacustrine settings, and made up of sediment shed from the San Juan uplift to the north and the Brazos-Sangre de Cristo uplift to the east. It was deposited mostly between ~64.5 and ~61 million years ago, during the early and middle Paleocene. The climate was humid and warm to hot. This unit interbeds with the
Roan Cliffs Roan Cliffs The Roan Cliffs are a series of desert mountains and cliffs in eastern Utah and western Colorado, in the western United States that are distinct from (but closely associated with) the Book Cliffs. While Roan Cliffs are "remote and inaccessible", the Book Cliffs run along the edge of the Castle, Gunnison, and Grand valleys and are therefore readily visible from populated areas (i.e., Price and Green River in Utah and Grand Junction in Colorado) and well traveled transportation corridors (i.e., I‑70, US‑6, US‑50, and US‑191). As such the Book Cliffs are much better known than the Roan Cliffs.