Largest Quake Since 1973 Rocks Colorado 5.3-magnitude shaker rattles homes near New Mexico border By Rob Quinn, Newser Staff Posted Aug 23, 2011 3:41 AM CDT Updated Aug 23, 2011 5:00 AM CDT 3 comments Comments This United States Geological Service map locates Monday night's earthquake. (United States Geological Service) (Newser) – The strongest earthquake to hit Colorado in nearly 40 years has shaken homes near the New Mexico border and caused rockslides along highways—but there have been no immediate reports of injuries. The 5.3-magnitude quake struck close to midnight, centered some 180 miles south of Denver, AP reports. Two milder quakes were felt earlier in the day in the area, which recorded a series of a dozen earthquakes a decade ago. "The area seems to be active again," says a US Geological Service geophysicist.