The rocks along Minnesota's North Shore of Lake Superior, for example, were created from cooling lava. Bentonite clay in southeastern Minnesota was formed from volcanic ash. Earthquakes Besides eyewitness accounts of earthquakes in Minnesota, geologists look at rock layers for evidence of these events. They can see that different layers do not always lay flat on top of one another. There are folds and breaks.
Geologists can also see evidence of earthquakes in Minnesota with the Midcontinental rift.
This rift, running from Minnesota to Kansas, is the result of the middle of the North American continent splitting apart. Rifting is the opposite of a mountain range forming. Instead of rock material being pushed up to form a mountain, rock material falls down when a wide split in the land is made. Molten material from deep within the earth rises up to fill in the gap. Mountains Geologists see patterns in rock layers and fault zones showing that rock layers were pushed on top of other layers.