Overview of recent mountain-building events in the Big Bend region, West Texas and Northern Mexico

The terrain of the Big Bend region, as well as locations of many ore bodies, hot springs, and the Rio Grande River, mostly result from two mountain-building events: Basin and Range extension that continues today, but also Rocky Mountain (or “Laramide”) contraction that ended 50 million years ago. Both events continued for tens of millions of years, producing complex arrangements of folds and faults throughout broad, overlapping zones extending from southern Mexico into Canada. Laramide contraction and Basin and Range extension are caused, at least in part, by changing plate interactions along the western margin of the North American plate. Two compilation maps of the Big Bend region, one showing Laramide structures and one showing Basin and Range structures, summarize current understanding. Panoramic photographs illustrate well-exposed structures in Big Bend National Park. An extensive reference list compiles work on Laramide and Basin and Range structures. Work to date, which includes recent detailed mapping in two small areas, emphasizes several points: a) Laramide structures in the Big Bend region include thick-skinned basement uplifts and coeval thin-skinned thrust belts, b) Map-scale and outcrop-scale folds formed during Basin and Range extension as well as during Laramide contraction, and c) Long-lived fault zones moved repeatedly during Laramide contraction and Basin and Range extension.