Artist Point is an outstanding viewpoint over the Grand Canyon of the Yellowstone, which has given its name to the park. After the Caldera explosion, about 600,000 years ago, this area was covered by subsequent lava flows which deposited rhyolite, an igneous volcanic rock. Hydrothermal alteration of different iron compounds gives the rock the range of colors we observe today. The canyon was probably formed from a combination of uplift and related faulting with intense erosion from river flows, especially at times of melt down after a period of glaciation. Glaciers may have plugged the river up-dip, trapping water and sediment alike. Abrasive gravel and sand abruptly released with ragging torrents of melt water further excavated this chasm. Waterfalls owe their existence to differential erosion between unaltered and hard rhyolite meeting softer hydrothermally-altered rhyolite.