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
Hole in the Rock (rock formation) them along the relatively benign terrain beneath the Straight Cliffs of the Kaiparowits Plateau. However, when this led them to the 1200-foot (400 m) sandstone cliffs that surround Glen Canyon, they needed a way to cross to the eastern rim. They found (and named) Hole in the Rock, a narrow, steep, and rocky crevice and sandy slope that led down to the river. Directly across the river was Cottonwood Canyon, a tempting route up to Wilson Mesa on the other side. They worked for months to prepare the road, using blasting powder to widen the upper section and hand chisels