Columnar Basalt - Geologist explains spectacular stone columns

Formation of Columnar Basalt is quickly described in this 2 Minute Geology episode.
Columnar Basalt is the result of cooling and cracking of an unusually thick basaltic lava flow. Columns are often 50 feet high or more.
The Columbia River Basalt Group of Washington and Oregon USA is a stack of more than 300 individual lava flows. The flows issued forth from deep fissures that began forming 17 million years ago in southeast Washington and northeast Oregon. Columns are well-developed in some of the flows and non-existant in many others. The Roza Flow is the most famous Columbia River Basalt flow for column formation. Notable columns around the world include Devils Tower in Wyoming and Giants Causeway in Ireland.