Copperopolis was founded by W.K. Reed and Thomas McCarty in 1860, who discovered vast copper deposits in the area. That same year, Hiram Hughes also discovered copper. Several extensive copper mines were established in what would be known as the Copper Cañon Mining District. These mines include the Napoleon Mine, the Keystone Claim, the Union Copper Claim, the Calaveras Claim, and the Empire Claim. The town adopted the name "Copperopolis" in 1861.
The mines were heavily utilized during the Civil War, when they were the principal copper producing section of the United States. The area was quickly transformed from rolling hills of grazing land into a booming community due to the need for copper for munitions and shell casings. Copperopolis rapidly became the second-most important copper district in the United States.
By 1861, over 28 businesses had been established, and by 1865, that number had increased to 90. The discovery of copper came at a time when the Mother Lode gold mines were almost dormant, and for seven years copper was the main focus of mining efforts in Calaveras County.
Copperopolis was staunchly pro-Northern doing the Civil War, a sentiment reflected in the names of many streets, establishments, and mines in Copperopolis: streets were named Union (now Main Street), Lincoln, Grant, and Sherman; the town also boasted a Union Hotel, Union Mine, and the Union Bridge. Only seven of the town's many buildings were brick, and in 1867, much of the town was destroyed by a catastrophic fire. The town was never completely rebuilt, and after the Civil War ended, the demand for copper began to decline though Copperopolis remained an important source of copper until the 1930s. In World War 2, the Keystone Mine briefly opened until 1945 and has remained closed. The boom and bust cycles in Copperopolis were closely linked to the need for war-time supplies.
Copperopolis has four buildings that are listed on the National Register of Historic Places: the Copperopolis Armory, the Copperopolis Congregational Church, the Honigsberger Store, and Reed's Store. Additional markers at significant sites include the Calaveras Telephone Company, The Old Corner Saloon, the Copperopolis Historical Plaza, and the Copperopolis Cemetery. A marker is also located here for Thomas McCarty, one of the town's founders. Copperopolis is also known as the town where Mark Twain supposedly wrote The Celebrated Jumping Frog of Calaveras County.
Today, the town remains inhabited, and as of the 2010 Census, had a population of 3,671 persons. Lake Tulloch also draws many visitors for its recreational opportunities.
Copperopolis is located on Highway 4, 12.8 miles west of Angels Camp and 40.2 miles east of Stockton. The historical marker is located at the State Department of Forestry Station, 375 Main Street.
Along with Mark Twain’s famous "The Celebrated Jumping Frog of Calaveras County" story that spun into an annual fair and Jumping Frog Jubilee, Calaveras County is rich with Gold Rush history and folklore. Remnants of the railroads and Hispanic culture add to the charm of the county located in the Sierra Nevada foothills. Calaveras Big Trees State Park, a preserve of Giant Sequoia trees, and the uncommon gold telluride mineral Calaverite was discovered in the county in 1861, and is named for it.
Calaveras is a Spanish word meaning "skull." The name was first given to the river because of the great quantities of human skulls found along the lower reaches of the river.
Calaveras County is famous for its lode and placer mines, and the largest gold nugget from the United States was taken from the Morgan Mine at Carson Hill in 1854, weighing 214 pounds. For many years it was the principal copper-producing county in California. Cement deposits from its vast limestone deposits has become one of the county's major industries in recent years.