PRELIMINARY 1:4,150 GIS MAP OF MESOZOIC AND CENOZOIC SEDIMENTARY UNITS AT GHOST RANCH, NEW MEXICO

Preliminary 1:4,150 GIS Map of Mesozoic and Cenozoic Sedimentary Units at Ghost Ranch, New Mexico

Ghost Ranch in Rio Arriba County, north-central New Mexico is an outstanding setting for undergraduate field courses in geology and paleontology. It is situated between the Valles Caldera and the San Juan Mountains, near the western edge of the Rio Grande Rift Valley. Students at Hanover College (Indiana) have been mapping six one-mile-square sections in this area using color aerial photographs for around 50 years. These sections were obtained from the GIS Data Depot. Our preliminary map (scale 1:4,150) covers approximately 10.4 km². It was created by geo-referencing four of the sections into GIS, and digitizing our field maps. At present ours is the first and only geologic map of the Ghost Ranch area at the 1:4,150 scale.

Map units include the Triassic “lower” Chinle Formation (Tcl), the “upper” Chinle Formation (Tcu), the Jurassic Entrada Formation (Je), the Jurassic Todilto Formation (Jto), the Jurassic Morrison Formation (Jmo), Quaternary landslide deposits (Qls), Quaternary Alluvium associated with seven strata terrace levels (Qal 1-7), and Holocene alluvium (Hal) including one terrace (Hal). Terrace deposits are widespread (though partially blanketed by aeolian sediment) and contain distinctive clasts assemblages including Precambrian igneous and metamorphic rocks derived from the San Juan Mountains. Also present are several normal faults showing substantial offset and with slickenside-bearing fault planes exposed in major ravines. Finally, the “upper” Chinle Formation hosts several world-famous vertebrate (including dinosaur) quarries.