Santa Fe formation in the Espanola Valley, New Mexico

Abstract

The type area of the Santa Fe formation (late Tertiary) is the region north of Santa Fe, New Mexico, between the Sangre de Cristo and Jemez mountains. The formation includes gravel, sand, silt, volcanic ash, and a little clay. Intraformational breccias are abundant in certain zones. Most of these materials were laid down as coalescing alluvial fans in a basin which, at its maximum, extended to the east and probably far to the west of the present limits of the formation. This alluvium was deposited by streams which flowed westward from highlands that bordered the basin on the east. Throughout most of the period of deposition these highlands were relatively low. During late Santa Fe time the eastern highlands stood at a somewhat greater elevation relative to the basin floor, and river gravels indicate that the center of the basin was occupied by a through-flowing river. The events of post-Santa Fe time have either removed or concealed all trace of the deposits laid down in the western part of the basin. Post-Santa Fe deformation has given the beds a general westward dip at angles of 5 to 10 degrees or more. At many localities the beds are displaced by normal strike faults, many of which are filled with conglomerate or sand dikes. Similar faults displace the unconformity which separates the formation from the older rocks to the east. Along their west border the Santa Fe beds are covered by the younger sediments and volcanics of the Jemez Mountains.