Quartz monzonite is a granitic rock that is primarily composed of quartz, plagioclase feldspar, and orthoclase feldspar. Other minerals, such as biotite and hornblende, are also typically present in small amounts. Abundant and widespread, the intrusive igneous rock may be found in tremendous masses in many mountainous areas. Quartz monzonite is also frequently involved in gorge formation since it is extremely resistant to weathering and stands tall as surrounding rocks erode away. Indeed, a prime example of this type of gorge is the Black Canyon of the Gunnison in Colorado, which owes its steep walls to the hardness of the rock that has successfully withstood the force of the Gunnison River for two million years.