The Colorado Lineament appears to be one of the source zones for the larger earthquakes of the west-central United States. As defined by Warner (1975), the lineament trends northeastward from northwestern Arizona to central Minnesota. Numerous Precambrian trends have been recognized along the lineament; some are reflected in the overlying strata. Mineralized areas such as the Colorado Mineral Belt, the Hartville iron deposits of Wyoming, and the Cuyuna Iron Range of Minnesota are associated with the lineament, which may represent a Precambrian continental plate boundary in the form of a wrench fault system (Warner, 1978). Between 1860 and 1875 about 18 earthquakes with epicentral intensity greater than or equal to VI and felt area greater than 25,000 km2 (10,000 mi2; equivalently a body-wave magnitude ges;4.5) had epicenters within the surface projection of the Colorado Lineament. All but a few of the remaining west-central earthquakes of this size can be associated with the Nemaha uplift, the Rio Grande Rift, the Wichita Mountain uplift and the Overthrust Belt. Although these latter structures have previously been recognized as source zones for larger earthquakes, the Colorado Lineament had not been so recognized.