The aerial distribution, dissection, and stratigraphic relations of Pliocene and younger mafic volcanic flows indicate that the Rio Grande in central New Mexico became a throughflowing drainage system during late Pliocene time (between about 3.0 and 4.5 m.y. ago). K-Ar dates indicate that the course of the Rio Grande was established more than 4.0 m.y. ago in central New Mexico and about 3.0+ m.y. ago in north-central New Mexico. The Ortiz geomorphic surface was probably graded to the ancestral Rio Grande about 3 m.y. ago and is considerably older than the Llano de Albuquerque surface. The central Rio Grande region has been warped and faulted since late Pliocene time. A complex fault block in the southeastern part of the Albuquerque-Belen Basin includes volcanic rocks more than 20 m.y. old that originated from southwestern New Mexico before rifting of the Rio Grande depression.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.