The occurrence of the mold of a rhinoceros in the pillows at the base of a basalt flow of the Columbia River Basalts near Blue Lake, Washington, is described and discussed. It is concluded that preservation of the rhinoceros mold is due to the special conditions causing the formation of the pillows in the base of the flow. Apparently the advancing lava flow encountered a shallow body of water, with a dead and bloated rhinoceros either upon the shore or floating on the water. The water caused the formation of the pillows at the base of the flow. The pillows retained sufficient plasticity to pack around the body of the animal but were rapidly cooled by the water so that they became rigid enough to preserve the mold thus formed. The entombed rhinoceros appears to be referable to the genus Diceratherium, suggesting an upper Oligocene or lower Miocene age for the containing lava. A restoration of the animal, based upon the mold, is presented.