The Galisteo Formation of North-Central New Mexico

Abstract

The Galisteo formation consists of from 900 to at least 4,000 feet of sandstone, sand, and clay, variegated in color, together with minor amounts of conglomerate, fresh-water limestone, and water-laid tuff, deposited by rivers in a broad, deep inland basin. The Galisteo was succeeded without interruption by deposition of the Espinaso volcanics. Fossil evidence indicates that the Galisteo formation is of Duchesnean (late Eocene or early Oligocene) age. At this time, north-central New Mexico had more rainfall than at present, but this may have been seasonal in nature. Forested highlands probably existed in the areas now occupied by the Sierra Nacimiento and the southern Sangre de Cristo Mountains. Large, perennial rivers flowed from the highland areas into and through the basin of deposition. Upper Cretaceous rocks were deformed and eroded prior to deposition of the Galisteo formation. Further warping occurred during Duchesnean deposition, but this deformation may have followed different lines. The southern Sangre de Cristo Mountains may have been rejuvenated at this time. The igneous rocks of the Ortiz Mountains and the Cerrillos Hills intrude the Galisteo formation and the Espinaso volcanics. These formations were deformed and eroded before deposition of the late Tertiary Santa Fe formation. The Rio Grande depression was not outlined until late Tertiary time.