The area in and around Mushroom Rock State Park is rich in early Kansas history and railroad lore. Accounts of the unique geologic formations at Mushroom Rock State Park began appearing in scientific and popular literature in the late 1860s. It is likely, though, that the site was a landmark for Native Americans and explorers long before Kansas became a state in 1861. Kit Carson reportedly referred to the area as his “favorite little place.”

The rocks, remnants of a deep layer of Dakota Sandstone, came to light as a result of survey work to lay a route for the Kansas Pacific Railroad. The rock formations were first noted in government survey reports in 1862 and the first geology reports appeared in 1866 and 1868. Stories of the railroad survey brought attention to Mushroom Rock, which was also called Pulpit Rock on Alum Creek. An article in Harper’s Weekly from July 15, 1867 was accompanied by an illustration of Pulpit Rock made from a survey engineer’s drawing. While the Kansas Pacific railroad later consolidated with the Union Pacific Railroad and no longer exists, the Union Pacific Railroad still runs just south of Carneiro, about ½ mile north of Mushroom Rocks.

Carneiro started its life as Alum Creek Station, a point where the Smoky Hill Trail crossed Alum Creek, which still runs through Mushroom Rock State Park. The Kansas City and Santa Fe Stage and Mail Line began traveling the trail in 1866. Carneiro itself was established in 1882 by sheep ranchers as a shipping point on the Union Pacific Railroad. At one point, the town included a hotel, stockyards, a school, a church, three general stores and a post office.

About six miles to the west, in the city of Kanopolis, are the four remaining buildings of Fort Harker, an active U.S. Army outpost from November 1866 to October 1872. The fort was one of the most important military installations west of the Missouri River. Its troops patrolled the overland trails in the region, protecting wagon trains and settlers from Native American resistance. It became a supply depot after the arrival of the Union Pacific Railroad in July 1867, and was used to distribute supplies to forts farther west.

Until 1963, the only way to see the rocks was by traveling a rough trail on privately-owned land. That year, Ellsworth County built a road through the area, allowing vehicle traffic. The Ellsworth County Historical Society secured five acres of the area, owned by two different parties, then deeded the property to the Kansas Park and Resources Authority, now the Kansas Department of Wildlife and Parks. The area became a state park on April 25, 1965. It is operated as a satellite of Kanopolis State Park.

Mushroom Rock State Park is located north of Kanopolis Reservoir. It can be reached via a short drive south from K-140 at Carneiro on 25th Road, or by driving west from K-141 via Avenue K, also a county road.