Uplift of North America
My books all describe terrain heavily influenced by the North American uplift. I first spent time on the subject when working on Palo Duro Vistas. The High Plains are capped by the Ogallala Formation, an immense sandstone and conglomerate body shed off the Rockies along a front from Nebraska to mid-Texas as the mountains rose.
In the Big Bend, the river follows a segment in the Rio Grande Rift Zone from El Paso to the Big Bend and another segment runs through Marfa down to join the other in Big Bend National Park. The rift zone is of an age with the uplift and is the result of the same forces.
It is not really possible to go into the intricacies of tectonic development that created the uplift in the books. It would take up too much space and would require massive duplication, so instead I created a pdf nearly three years ago to explain the background to those readers that want to follow up. I have updated it slightly today (1/4/09).