Pass Creek Road is a hidden gem in western Huerfano County. It crosses the Sierra Blanca ridge from Costilla County in the south to the Upper Huerfano River Valley in the north. Along the way it passes through a simply beautiful countryside with some very interesting geology.

The mountains to the west of Pass Creek are old, about 1.7 billion years old, part of the Colorado Orogeny upthrust that put Mt. Blanca, California Peak, the Front Range, and most of the Wet Mountains in place. The mountains to the east of Pass Creek are young, about 25 million years old, all part of the igneous intrusion that we call Mt. Mestas, Silver Mountain, Rough Mountain, and the Sheep Mountains. This area was once part of the Grayback Mining District, with most of the activity going on in the mountains to the west.

Riding through here is actually riding along one of the fault lines that formed the Sangre de Cristo Mountains. The road crosses back and forth through upthrust plates of Dakota sandstone and in between vertical granite walls. The Dakota sandstone testifies to the upward thrusting of the ground: this was horizontal sandstone (ocean bottom) until it was turned up by action along the fault line. The vertical granite walls testify to the flow of molten magma in the cracks in the ground caused by the action along the fault line. Of course, all this activity happened 25 or so million years or more ago. And what we have now...