Tertiary Geology of the San Acacia Area New Mexico

Abstract

The San Acacia area includes a part of the Rio Grande depression in central New Mexico and is underlain predominantly by basin deposits of late Tertiary age, the Popotosa and Santa Fe formations. The Popotosa formation, heretofore undescribed, is a tuffaceous fan deposit which was laid down in an enclosed basin during late Miocene (?) time. The Santa Fe formation, of Pliocene and late Miocene (?) age, was deposited in several contemporaneous and contiguous basins, some of which had exterior and others interior drainage. A reconstruction of the paleogeography of the area in Santa Fe time is presented. The Tertiary rocks are downfaulted as a graben between highlands composed predominantly of pre-Tertiary rocks. Minor horsts are found within the Tertiary rocks. There were at least three, and possibly five, episodes of deformation during Tertiary time.