On geological time scales, few things are permanent. This is as true in our desert as anywhere else. Whereas today the Rio Grande can almost be considered as a defining character of the northern desert region, for many millions of years, it was no river at all. Instead, a series of unconnected geologic basins supported playas and, possibly upon occasion, permanent lakes.
The stretch from Santa Fe to Socorro, New Mexico, finally joined the
Socorro to El Paso basin only sometime after about 3.4 million years ago. During wetter
times, a large, shallow lake, Lake Cabeza de Vaca, formed in the northern Chihuahua and
southern New Mexico and El Paso region. These southern basins slowly filled with
sediments, eventually reaching the level of the flat surface into which we see the
present-day Rio Grande Valley incised. Later, sometime before about 750 thousand years
ago, Lake Cabeza de Vaca broke through to drain to the southeast—for the first time,
the Rio Grande ran as a connected river all the way from southern Colorado to the Gulf
of Mexico.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.