Brazos Mountains to 55 million years ago during the Laramide orogeny. To the east and northeast lie the Sangre de Cristo Mountains which share a similar geological history. The Brazos Cliffs, which form a dramatic backdrop to Tierra Amarilla, are formed of Precambrian quartzite. Brazos Mountains The Brazos Mountains is a range in far northern Rio Arriba County, in northern New Mexico in the southwestern United States. A high crest runs from the border with Colorado for over in a south-southeasterly direction. The high point of the range at is on Grouse Mesa, at the Brazos Benchmark. Two miles (3 km) to
Straight Cliffs Formation is the partial lateral equivalent of the Mancos Shale formation further east. The Straight Cliffs Formation is latest Turonian to early Campanian in age. The stratigraphy of the formation was initially studied for its coal resources and has more recently been studied as an analog for petroleum reservoirs. Consequently, the stratigraphy of the Straight Cliffs has been analyzed in detail. The Straight Cliffs Formation was deposited in the Kaiparowits Basin of the Western Interior Seaway. The basin received sediment from the Mogollon highlands, the Sevier fold-thrust and the Cordilleran volcanic arc. The Mogollon highlands were mountains in central Arizona. The