Yes, the cave is natural.
Jewel Cave was set aside as a National Monument by Theodore Roosevelt on February 7, 1908.
Jewel Cave National Monument is located in the Black Hills of South Dakota, near the town of Custer. It is situated approximately 13 miles west of Custer and is part of the larger Jewel Cave System, which is one of the longest caves in the world. The monument offers various tours and recreational opportunities, showcasing its stunning formations and diverse ecosystems.
John Hancock Building in Chicago
Russell Cave National Monument was created in 1961.
Timpanogos Cave National Monument was created in 1922.
Carlsbad Cave National Monument was created in 1923.
The area of Russell Cave National Monument is 1,254,525.490944 square meters.
The area of Timpanogos Cave National Monument is 1,011,714.1056 square meters.
Russell Cave National Monument
yes
Yes, there are monuments in South Dakota, including:1) Mount Rushmore National Memorial, America's "Shrine of Democracy", is part of the National Park Service.2) Crazy Horse Memorial, owned by a non-profit foundation, is a way to honor the culture and traditions of North American Indians.3) Jewel Cave National Monument, part of the National Park Service, is the second longest cave in the world.4) Hugh Glass Monument near Shadehill, South Dakota. Hugh Glass was nearly killed by a grizzly bear here in 1823. He revived and crawled, with a broken leg, infection and fever, 200 miles to safety.5) The Geographic Center of the Nation Monument, a 21-foot diameter structure made of etched-SD granite marks Belle Fourche as the town closest to the geographic center of the 50 states.6) Wild Bill Monument erected in place of original tombstone for James Butler "Wild Bill" Hickok in Deadwood, South Dakota.7) Friendship Monument or Friendship Tower erected on Mount Roosevelt near Daedwood, SD in memory of Theodore Roosevelt.8) Preacher Smith Monument near Deadwood, SD.9) There are several memorials/monuments on the grounds of the South Dakota State Capitol in Pierre, SD including the Fighting Stallions Memorial, the World War II Memorial, the Korean War Memorial, and the Vietnam War Memorial.And many more....
C. F. Dyer has written: 'Geology and occurrence of ground water at Jewel Cave National Monument, South Dakota' -- subject(s): Groundwater, Geology