A magnitude 5.3 earthquake struck near Trinidad, Colorado last night around 11:30 pm, local time, just north of the New Mexico border. There had been a magnitude 4.6 quake earlier in the day in the same area, and there have been a number of smaller aftershocks overnight. There are some reports of damage to homes and rockslides on highways. [right, quake location map from USGS]
It's apparently the largest quake in Colorado since a magnitude 5.7 event in 1973, north of Grand Junction in western Colorado.
update 9am: I asked Colorado State Geologist Vince Matthews the source of earthquakes in this area. He referred me to their 2002 publication, page 8: "The detailed studies of the fault under Segundo showed that the earthquakes are occurring on a 6 km long fault. A fault of this length is capable of generating a magnitude 5.8 earthquake (Wells and Coopersmith, 1994)." [http://geosurvey.state.co.us/pubs/Documents/rtv5n2.pdf]