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
Brazos River tributaries of the Upper Brazos that rise on the high plains of the Llano Estacado, flowing southeast through the center of Texas. Another major tributary of the Upper Brazos is the Clear Fork Brazos River, which passes by Abilene and joins the main river near Graham. Important tributaries of the Lower Brazos include the Paluxy River, the Bosque River, the Little River, Yegua Creek, the Nolan River, the Leon River, the San Gabriel River, the Lampasas River, and the Navasota River. Initially running east towards Dallas-Fort Worth, the Brazos turns south, passing through Waco and the Baylor University campus, further