GEOLOGIC RESEARCH IN THE SANTA FE NATIONAL FOREST, JEMEZ MOUNTAINS, NEW MEXICO

The New Mexico Bureau of Geology and Mineral Resources, in cooperation with the U.S. Geological Survey (STATEMAP) and the U.S. Forest Service, has produced sixteen new 1:24,000 scale geologic maps in the Jemez Mountains, New Mexico, during the last five years. These maps, at 400% the scale of previously available mapping, greatly improve our understanding of the rich, complex Proterozoic to Pleistocene geologic history of this mountain range, which lies at the intersection of the Colorado Plateau, the Rio Grande rift, and the Jemez lineament. The Santa Fe National Forest covers the majority of the Jemez Mountains.

Several significant research initiatives developed during the mapping project. Of particular current relevance are observations applicable to hydrologic and land use issues in this important recharge region of the Albuquerque metropolitan area. These include: 1) much better definition of pre-Bandelier Tuff topography, including recognition and characterization of river-channel deposits below and within the 1.2 to 1.8 Ma Bandelier and San Diego Canyon tuffs, (2) recognition of a 10-km long Pliocene (?) landslide involving 8.9 Ma Paliza Canyon andesite, and both over- and underlying units, (3) better definition of structural zones, including a previously unrecognized fault system sub parallel to and east of the Jemez Fault zone; (4) recognition that volcaniclastic sediments comprise much more of the early Jemez Mountain (8 to 10 Ma) volcanic pile than previous maps show (~50%); and (5) recognition of late Oligocene to early Miocene volcaniclastic sediments in the southwest Jemez Mountains. In addition, improved geochronology has led to the identification of discrete volcanic centers and eruptive trends not recognized in earlier work