Day 1 road log: The Rio Grande Rift, the southern Albuquerque Basin and the southern Manzano Mountains
— D.W. Love, K.E. Karlstrom, B.A. Frey, Lucas, S.G., Williams, S., P. Miller, M. Holland, M.L. Williams, M Heizler, and T. Grambling

Day 1 of this field conference covers some of the longest geologic time and widest tectonic variation of the trip. We begin on the Santa Fe Group sediments of the Albuquerque Basin, focusing on the drainages and sediments in the vicinity of Black Butte (Turututu), which mainly are sourced in the Manzano and Los Pinos mountains. As we move eastward and upward, we cross the Montosa fault into the Manzano Mountains where we view Precambrian metavolcanic, metasedimentary, and intrusive rocks, which are capped by Pennsylvanian and Mississippian sedimentary rocks. Throughout the day, we consider the complicated tectonic landscape of the Rio Grande rift, a north-south trending zone of extension that saw its main activity in the Miocene. The rift created several basins from Colorado to southern New Mexico, including the Albuquerque Basin (Fig. 1; Plates 1, 2, 3), by dropping down some of the same Precambrian bedrock and Mesozoic and Paleozoic sediments we will see in the uplifted Manzano Mountain rift flank. This basin became the catchment for thousands of feet of sediment in the Santa Fe Group (Russell and Snelson, 1994; Ricketts and Karlstrom, this volume).

Stop 1 will be at a roadside relay tower where we will discuss geologic and geographic features in the area. From here, we can easily view Turututu, a butte made up of ash-flow tuffs and basaltic andesite, one of the northeastern-most exposures of the Mogollon-Datil volcanic field, and stand on the southern extent of the Albuquerque Basin. We will describe recent geomorphic work at this location, review interpretations of the COCORP seismic lines, and discuss interpretations of the underlying rift tectonic throughout the area.

Stop 2 will be a unique opportunity to access BNSF railway property and view the engineering feats achieved by the Atchison Topeka & Santa Fe railroad as we pass under railway bridges to reach the entrance of Sand Canyon. The railway and its bridges have had a major impact on the economy of Belen and the rest of the southwestern United States as part of the railroad’s Belen Cutoff. As we cross under the bridges and enter Sand Canyon, we will view the Laramide Montosa fault monocline on the east side of the Manzano Mountains. In this canyon, flat-lying Paleozoic beds dominate the eastern skyline, and the same beds are upturned in the center of the local drainage to form the synclinal hinge of the Montosa monocline.

Estadio Canyon will be the location for lunch and the remainder of the day’s activities, designated Stop 3. The itinerary for Stop 3 is a one-mile hike, with easy and strenuous options, involving a series of eight stations where student guides will show the complex Precambrian structural components of the canyon, including impressive outcrops of folded quartzite and preserved primary features, such as cross bedding, that will guide our interpretations. Discussions will focus on the metamorphic and deformational aureole of the 1.45-Ga Priest pluton and a model for syntectonic-emplacement of the pluton. The hike will begin at the western edge of the pluton’s influence and end at the contact between the pluton and the metasedimentary rocks of the aureole.