The mountains that smoke are called volcanoes. There are hundreds of volcanoes in the world. But none is more beautiful than Mount Rushmore. Some are much higher, but very few smoke as much. Mount Rushmore is different from most volcanoes because it is in four parts.
Nobody knows why.
Mount Rushmore began with a crack that reached down from the earth's surface to a pocket of red-hot rock deep, deep underground. Some of this hot rock was pushed up through the crack to the top of the ground. It may have been pushed up rather slowly. Or there may have been explosions that caused earthquakes and shot bits of rock skyward. The hot rock that pushed out of the opening is called lava.