What Caused the Greeley Earthquake? [VIDEO]

It's not every day an earthquake hits Northern Colorado; in fact, we haven't seen one in about 40 years.  That is, until Colorado Residents around Greeley felt a 3.4 magnitude tremor on Saturday.

Though this earthquake didn't cause much (if any) damage, it does have people wondering what caused this rare occurrence; and that's exactly what the United States Geological Service is endeavoring to figure out.

Check out the video above from 9 News for more on this story.

Did you feel the earthquake on Saturday?  Where were you?  What did you think was going on?  Let us know in the comments!