The Wind/Bighorn River is an 'antecedent stream'

In a recent letter to the editor, Duane Richter questioned how the Wind River was able to start at the top of the Owl Creek Mountains in order to carve out the Wind River Canyon. The answer to this perplexing question is that it didn’t. The Wind/Bighorn River is a classic example of an antecedent stream. An antecedent stream is defined as a stream which pre-existed local uplift and maintained its original course and grade by incising its channel at approximately the same rate as the topography was rising. The Wind River Canyon is correctly referred to as an antecedent valley since it was eroded by, and contains, an antecedent stream. Most of the geologic structure and consequent topographic features we have in the Bighorn Basin have their origins in the Laramide Orogeny which was initiated about 70 million years ago. This amount of geologic time has provided the Wind River more than enough time to maintain its grade as the Owl Creek Mountains were uplifted.

In contrast to an antecedent stream is the more common “consequent stream.” As the name implies, a consequent stream’s course and grade is a consequence of the existing topography. Examples of consequent streams are the meandering stream courses on the north slope of Nostrum Mountain located just west of the Wind River Canyon. These consequent streams are beautifully-portrayed at low sun angles when viewed from the Thermopolis area.