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Santa Elena Canyon in Big Bend (C)
There are many fine things to see in the Big Bend area, but I think that the mouth of Santa Elena Canyon is the centerpiece. The Rio Grande emerges from a nearly vertical wall, some 1500 feet high. The river has cut this huge gash in the limestone, working slowly and steadily over the millennia.
You are looking upstream along the river. The river makes a sharp right turn, and then flows for several miles close to the base of the wall. In recent years, the water has been ten feet higher than it is shown here, even with all the dams and diversions upstream.
The vertical wall is what is known as a block fault, caused by shifting of the earth’s crust, where part of the surface tries to ride up over another part. It is not known whether this happened slowly, while the river cut through it (as happened at Grand Canyon) or whether it happened more rapidly, and the river was dammed for a while until it found a place to start cutting.