A photo of Santa Elena Canyon.

The chasm-like passage of Rio Grande through Santa Elena Canyon suggests that the river channel is antecedent to ridge (Sierra De Santa Elena). An antecedent stream is a stream passage that existed on an earlier landscape that was then raised. As erosion wears away the landscape surface, the river channel cuts downward through structures buried below the surfaces. 

Terlingua Creek enters the Rio Grande from the valley to the right.