Lower Yellowstone Falls, Yellowstone river. These 33 meter high falls are the largest volume falls in the Rocky Mountains of the USA. The yellow rock around the river is a thermally degraded (hydrothermally altered) rhyolite. The trees are lodgepole pines. At the right time of day the sunlight creates a rainbow in the spray. Yellowstone Park is the world's first National Park and this is one of its jewels.