Notch Peak, Utah

Lenticular cloud parked next to Notch Peak. (photo by Shawn Grant)

Geological Info:

Notch Peak is composed of 500-million-year old limestones and dolomites of the Notch Peak, Orr, and Weeks Formations. A 17-million-year old granite intrusion (sill) crops out at the base of this limestone sequence. Following the pattern found across the Basin and Range Province from western Utah to eastern California, a north-south oriented high-angle fault uplifted the mountain front on the west side of Notch Peak. This uplift allowed erosion to carve the peak’s great cliff.

At least two factors contributed to make Notch Peak’s north-face cliff grander than any other in the Basin and Range Province. First, the cliff is composed of a nearly uninterrupted sequence of strong, weather-resistant, massive limestone and dolomite beds that generally lack shale or other weak layers. Where significant shale beds do exist, they create a small bench near the top of the Orr Formation approximately 1,500 feet below the peak’s summit.

Secondly, the massive limestone and dolomite bedding is nearly flat and horizontal (not folded). Tectonic folding could have resulted in fractures that weaken rock layers. Similarly, tectonic compressional forces have not thrusted these rock layers over one another. Elsewhere in the Basin and Range past episodes of tectonic folding and thrusting have fractured and weakened otherwise similar formations and thereby reduced their integrity and ability to form towering cliffs. Though there is no clear evidence for such, an east-west oriented fracture (perpendicular to the range-front fault) could have provided a zone of weakness contributing to the north-facing orientation of the peak’s greatest cliff.