Carrizo Mountains

The Carrizo Mountains (36°50' N, 109°7'W) are a small range 15 to 20 km (9 to 12 miles) in diameter located on the Colorado Plateau in northeastern Arizona. The range is about 20 km southwest of the Four Corners. The highest summit, Pastora Peak, is 2869 meters (9412 feet) in elevation, whereas elevations on the surrounding plateau are near 1800 meters (5900 feet).

The mountains are within the Navajo Nation. Teec Nos Pos, Arizona, the closest community, is several km to the north, and had about 800 inhabitants in the year 2000.

Geology

The mountains are formed about igneous rocks that intruded and uplifted Permian through Cretaceous sedimentary rocks. The most common igneous rock type is porphyritic hornblende diorite. Intrusive forms include laccoliths, stocks, sills, and dikes. Radiometric ages of the igneous rocks range from 70 to 74 million years.

The similar igneous-cored mountain ranges on the Colorado Plateau fall into two age groups. The Henry Mountains, the Abajo Mountains, and the La Sal Range formed about igneous rocks 20 to 31 million years in age, and so they are distinctly younger than the major intrusions of the Carrizo Mountains. Radiometric ages of igneous intrusions in Sleeping Ute Mountain are essentially identical to those of the diorite intrusions in the Carrizos. Both the Carrizo Mountains and Sleeping Ute Mountain are in a southwest extension of the Colorado Mineral Belt, a feature defined partly by igneous rocks that are associated with ore deposits. Nonetheless, no large ore deposits have been found within the igneous rocks of the Carrizos. Small deposits of uranium plus vanadium and of copper plus silver have been found in the sedimentary rocks of the Morrison Formation in this mountain range.

References

* Steven C. Semken and William C. McIntosh, "40Ar/39Ar age determinations for the Carrizo Mountains laccolith, Navajo Nation, Arizona". New Mexico Geological Society Guidebook, 48th Field Conference, p. 75-80, 1997.
* Virginia T. McLemore and William L. Chenoweth, "Occurrence of copper and silver at the Carrizo copper mine in the Carrizo Mountains, Apache County, Arizona". New Mexico Geological Society Guidebook, 48th Field Conference, p. 269-272, 1997.