Map Courtesy of Montana Bureau of Mines and Geology

This geology map of the area shows the relationship between the Highwood Volcano (red patchy area in middle), the dikes (red lines extending from volcano) and the laccoliths. Magma beneath the volcano caused cracks in the surrounding rock, and then moved into these cracks - creating the dikes. Occasionally magma in a dike pooled beneath the surface, creating a laccolith. Tens of millions of years of erosion wore down the surrounding sedimentary rock, exposing some of the dikes as ridges and some of the laccoliths as buttes. If you have access to Google Earth, take a look at this area and see if you can spot the dikes. BACK

Web Site Created by Rod Benson
Earth Science Teacher at Helena High School

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