Columnar jointing is common in intrusive bodies formed at comparatively shallow depths. _The following new material has been added to this booklet by the National Park Service (Devils Tower National Monument, 1985)_ The most recent in depth, geologic study of Devils Tower was done by Don L. Halverson (1980) and presented in a dissertation, to the Graduate Faculty of the University of North Dakota. He stated that, “The Missouri Buttes and Devils Tower, however, are necks of extinct volcanoes which have been exposed by erosion. This theory was first proposed by Carpenter (1888) and later expanded by Dutton and Schwartz (1936). The material which fed these volcanoes came from a minimum depth of 18 km. Evidence for this conclusion is listed in the following statements: 1. The alloclastic breccia in the vicinity of Devils Tower and the Missouri Buttes is definitely igneous in origin and probably represents periods of violent eruption. 2. A very definite similarity exists between these two features and the volcanic necks in the Taylor Mountain area of New Mexico. 3. The distinctive columns with basal flare are also found in the volcanic necks of the Taylor Mountains (Dutton and Schwartz 1936), but have not been reported in columnar-jointed laccoliths. 4. The Missouri Buttes and Devils Tower were intruded directly through horizontal sediments without disrupting them, even in the immediate vicinity of the igneous bodies. 5. Recent research indicates that many of the laccolithic intrusions in the Black Hills region may have been less passive than previously considered. Sundance Mountain may be a mixed volcanic cone consisting of welded ash fall, massive quartz latite, and ash flow tuffs. Nearby Sugarloaf Mountain is composed of layered tuffs (Fashbough 1979). 6. Collapse of materials into partly evacuated reservoir chambers accounts for the depressions surrounding the Missouri Buttes and Devils Tower. The 90 m of depression at the southern end of the Buttes is difficult to explain with a laccolithic model. 7. Flow directions deduced from oriented thin-sections and field observations indicate mostly vertical flow. It must be noted that in both igneous bodies orientation of some grains is horizontal; this could, however, simply indicate turbulent flow. 8. The stability field for the analcime-liquid system is 5 kbar minimum (Roux and Hamilton 1976), which indicates that the original melt of Devils Tower and Missouri Buttes rock had to originate at a minimum depth of 18 km. 9. It is unlikely that magma which had ascended from great depths and had just penetrated the resistant Hulett Member of the Sundance Formation, as well as the Lakota and Fall River