Basin and range, and to a lesser extent laramide, structures control the topography of the trans-pecos region. However, the area has experienced repeated deformation since the preCambrian. Major tectonic events occurred in the preCambrian, late Palezoic, early to middle Mesozoic, late Mesozoic to early Cenozoic, and late Cenozoic. Structures and trends established in earlier events were later reactivated. Trans-pecos structure is thus a summation of many events as illustrated in the accompanying map.