The hot spring deposits at mammoth hot springs, yellowstone national park, are travertine. what rock probably lies somewhere beneath the hot springs?

The type of rock lying beneath the hot springs is a molten rock, or mixture of liquefied hot rocks, better known as magma. This is actually the source of the heat for the hot springs in Yellowstone, as well as for the other geothermal features. Much of Yellowstone lies on a gigantic volcanic crater.