“…In addition to known prominent shear zones in Colorado, the interpretation of magnetic data implies the presence of abundant northeast-trending shear zones throughout the entire southern Rocky Mountain region (Carol Finn, personal communication, 2001). These shear zones were reactivated repeatedly in the Phanerozoic, as shown by mylonitic shear fabrics, late faulting and brittle fracturing, and by alignment of younger intrusions and structural and topographic features (Sims et al 2001). In addition to having been a major factor in localizing the CMB, several speci®c features can be shown to be aligned along major Mesoproterozoic shears.…”