Yellowstone’s Grand Loop Road headed from Mammoth Hot Springs to Norris Jct.
deposits it on the surface forming these huge terraces. As we leave Mammoth Hot Spring heading south, the road passes thru Golden Gate. The road passes byObsidian Cliff, a “mountain of glass”. This rock formation is the same as rhyolite, but in this case, the rhyolite cooled so quickly that it did not crystalize. Instead, black glass was formed.