This is the heart of the continent, in the Great Plains that is forging the American spirit with the Westward Expansion , the construction of the railroad, the discovery of oil , civilization has died giving birth a new world. Great Plains have been transformed into a half-century , plows have eaten the rolling grasslands replaced by cereals , bison gave way to cattle herds and huge dams have emerged and domesticated rivers irrigator tirelessly over vast expanses grown , emptying all watercourses draining lakes. Groundwater – which runs from Texas to the Dakotas – is in peril. Mount Rushmore National Memorial, carved jackhammer and dynamite in the Black Hills granite busts representing the four presidents – George Washington , Thomas Jefferson, Abraham Lincoln and Theodore Roosevelt – is a symbol of American democracy. Light and shadows play on the heads of 18 meters high , animated expressions and enhance the spectacular aspect of this monument. The magnificent beauty of the Badlands National Park, attracts with its bare tertiary platforms , eroded by weather and notched winding gorges, and forcefully expressed when the sun floods the edges of an orange color, blacken the folds of the rock side by side with the green hills , the symbol of a vanished civilization. After a treaty with the Indians in 1868 , guaranteeing the inviolability of their territory not met following the discovery of gold in the Blacks Hills. Rapid City grew and became the 2nd city in the state and a very important commercial center . Custer State Park, created in 1910 is one of the largest parks of the United States , bison, reintroduced Dakota form a solid herd. South of the park is the Wind Cave National Park , a maze of spectacular caves . Crazy Horse Memorial in honor of the great Sioux chief , Ogallala, Indian resistance figure was sculpted in 1942 by Korčák Ziolkowski . Jewel Cave National Monument is a set of underground tunnels 106 kms decorated with beautiful colored calcite formations .