Devils Tower. View of Devils tower, a basalt outcrop in Wyoming, USA. A faint rainbow is seen to its left. This massive rocky tower rises almost 300 metres above the plain. It was formed by the cooling of a plug of underground magma (molten rock) produced by a volcano around 60 million years ago. Erosion of the softer surrounding soil and rock over the centuries slowly exposed the hard rock, causing it to project above the surface.
