Jerome, Arizona

Jerome is a town in the Black Hills of Yavapai County in the U.S. state of Arizona. Founded in the late 19th century on Cleopatra Hill overlooking the Verde Valley, Jerome is approximately 100 miles (160 km) north of Phoenix along State Route 89A between Sedona and Prescott. Supported in its heyday by rich copper mines, it was home to more than 10,000 people in the 1920s. As of the 2020 census, its population was 464.

The town owes its existence mainly to two ore bodies that formed about 1.75 billion years ago along a ring fault in the caldera of an undersea volcano. Tectonic plate movements, plate collisions, uplift, deposition, erosion, and other geologic processes eventually exposed the tip of one of the ore bodies and pushed the other close to the surface, both near Jerome. In the late 19th century, the United Verde Mine, developed by William A. Clark, extracted ore bearing copper, gold, silver, and other metals from the larger of the two. The United Verde Extension UVX Mine, owned by James Douglas Jr., depended on the other huge deposit. In total, the copper deposits discovered in Jerome's vicinity were among the richest ever found.

Jerome made news in 1917 when labor unrest involving the Industrial Workers of the World (IWW) led to the expulsion at gunpoint of about 60 IWW members, who were loaded on a cattle car and shipped west. Production at the mines, always subject to fluctuations, boomed during World War I, fell thereafter, rose again, then fell again during and after the Great Depression. As the ore deposits ran out, the mines closed for good in 1953, and the population dwindled to fewer than 100. Efforts to save the town from oblivion succeeded when residents turned to tourism and retail sales. Jerome became a National Historic Landmark in 1967. By the early 21st century, it had art galleries, coffeehouses, restaurants, a state park, and a local museum devoted to mining history.

Jerome is about 100 miles (160 km) north of Phoenix and 45 miles (72 km) southwest of Flagstaff along Arizona State Route 89A between Sedona to the east and Prescott to the west. The town is in Arizona's Black Hills, which trend north–south. The town lies within the Prescott National Forest at an elevation of more than 5,000 feet (1,500 m). Woodchute Wilderness is about 3 miles (5 km) west of Jerome, and Mingus Mountain, at 7,726 feet (2,355 m) above sea level, is about 4 miles (6 km) south of town. Jerome State Historic Park is in the town itself. Bitter Creek, a tributary of the Verde River, flows intermittently through Jerome. East of Jerome at the base of the hills are the Verde Valley and the communities of Clarkdale and Cottonwood, site of the nearest airport.

Most of Cleopatra Hill, the rock formation upon which Jerome was built, is 1.75 billion years old. Created by a massive caldera eruption in Precambrian—elsewhere more narrowly identified as Proterozoic—seas south of what later became northern Arizona, the Cleopatra tuff was then part of a small tectonic plate that was moving toward the proto-North American continent. After the eruption, cold sea water entered Earth's crust through cracks caused by the eruption. Heated by rising magma to 660 °F (350 °C) or more, the water was forced upward again, chemically altering the rocks it encountered and becoming rich in dissolved minerals. When the hot solution emerged from a hydrothermal vent at the bottom of the ocean, its dissolved minerals solidified and fell to the sea floor. The accumulating sulfide deposits from two such vents formed the ore bodies, the United Verde and the UVX, most important to Jerome 1.75 billion years later.

These ore bodies formed in different places along a ring fault in the caldera. About 50 million years after they were deposited, the tectonic plate of which they were a part collided with another small plate and then with the proto-North American continent. The collisions, which welded the plates to the continent, folded the Cleopatra tuff in such a way that the two ore bodies ended up on opposite sides of a fold called the Jerome anticline.

No record exists for the next 1.2 billion years of Jerome's geologic history. Evidence from the Grand Canyon, further north in Arizona, suggests that thick layers of sediment may have been laid down atop the ore bodies and later eroded away. The gap in the rock record has been called the Great Unconformity.

About 525 million years ago, when northern Arizona was at the bottom of a shallow sea, a thin layer of sediment called the Tapeats Sandstone was deposited over the Cleopatra tuff. Limestones and other sediments accumulated above the sandstone until about 70 million years ago when the Laramide Orogeny created new mountains and new faults in the region. One of these faults, the Verde Fault, runs directly under Jerome along the Jerome anticline. Crustal stretching beginning about 15 million years ago created Basin and Range topography in central and southern Arizona, caused volcanic activity near Jerome, and induced movement along the Verde Fault. This movement exposed the tip of the United Verde ore body at one place on Cleopatra Hill and moved the UVX ore body to 1,000 feet (300 m) below the surface. Basalt, laid down between 15 and 10 million years ago, covers the surface beneath the UVX headframes and Jerome State Historic Park. The basalt, the top layer of the Hickey Formation, caps layers of sedimentary rock.