The Devils River uplift is inferred to continue westward into Trans-Pecos Texas. Both the known Devils River uplift and the Tascotal uplift are bounded on the north by east-west fault zones (Chalk Draw and Carta Valley fault zones) separating them from Late Pennsylvanian clastic foredeep basins (Marfa and Val Verde basins). The exposed, much-shortened Marathon thrust belt may have been emplaced in the earliest Permian by gravity gliding. Meager evidence suggests that the Devils River block represents a Cambrian or Infracambrian rift and that the uplift is an aulacogen. The early Cambrian continental margin probably continued southwest into Mexico but has been displaced by Mesozoic left-lateral movement.