The USGS Earthquake Hazards Program has compiled a database of earthquake faults in the United States which are believed to be the sources of earthquakes with magnitudes greater than 6 during the past 1,600,000 years. Detailed descriptions of many of the faults is provided via an online database linked to the fault lines in Google Earth.
The original data and KML files were created by the USGS and their partners. I reorganized the original files to make this dataset a little more user friendly. This is about a 7 megabyte download and might take a minute to process.