Structural zones transecting the southern Rio Grande Rift - Preliminary observations
— Patricia Wood Dickerson

At least thirteen east-west trending zones that transect the Trans-Pecos portion of the Rio Grande rift between 29° and 31°30' north latitude (fig. 1) have been loci, in whole or in part, for repeated disruption of varying types during the last 1500 m.y. Evidence for these pervasive weak zones includes fold and fault patterns, aligned volcanic centers and intrusions, trends of evaporite diapirism and mineralization, gravity and magnetic anomalies, heat flow patterns and thermal springs, and physiography. They have responded differently to the varying stress regimes applied across the region through time, and it is proposed here that since late Miocene time at least one of the zones may have served as an intracontinental transform crossing the Rio Grande rift.

As Muehlberger discusses the tectonic history of the region elsewhere in this guidebook, I will review only the principal deformational periods and styles, emphasizing effects observable along the east-west structural zones designated in Figure 2.