ABSTRACT
Reconnaissance of the Lower Paleozoic sediments diagonally crossing the northern Sangre de Cristo Range of southern Colorado disclosed an imbricate zone of east-dipping thrusts associated with parallel, normal, and transverse faults on both sides of the range. Open folds sharpen southeastward from Wellsville, breaking into thrusts causing several repetitions of the section, then dying out without transition through folds. The folds at Orient also break into thrusts to the north and appear to denote the southern end of the thrust zone. Two areas offer evidence for shallow thrusting confined to the Lower Paleozoic. Transverse faults commonly displace thrusts. The steep western slope of the range is considered the scarp of a normal fault.
Four ages of Laramide and Tertiary deformation are recorded. The zone of westward-directed thrusting is part of a broader zone including the Pleasant Valley fault and similar thrusts west of the San Luis Valley. This zone is probably continuous with the early Eocene London-Weston thrust belt of South Park and the Mosquito Range. The northeast-directed folds and thrusts of the Sangre de Cristo Range south of Orient have no counterpart in the northern range. Large normal faults in the Wellsville-Orient thrust zone indicate vertical uplift of a pre-Cambrian area and are correlative with late Eocene uplift on the south. Downfaulting of the San Luis Valley from Oligocene to Recent outlines the present trend of the range and explains its divergence from the zone of thrusting.
