Third-day road log, from Alpine, Arizona, to Luna, Reserve, Apache Creek, Horse Springs and Datil, New Mexico
— James C. Ratte, D. J. Bove, S. M. Cather, R. M. Chamberlin, S. G. Crews, and W. C. McIntosh

On Day 3, the trip departs from the Alpine, Arizona Country Club, where we will have assembled for breakfast, starting at 6:00 a.m. Arizona Time! (7:00 a.m., NM time). Starting at Alpine, in the footwall of the Reserve graben system, the Third-Day route follows US-180 east, via Luna, New Mexico, descending into the Reserve graben across several tilted, halfgraben blocks. Between Luna, and the junction of US-180 and NM-12, we pass through the recent landslide areas in Mail Hollow and Dry Leggett Canyon, which disrupted traffic for several weeks in Fall 1992. At the junction of US-180 and NM-12, we tum north and follow NM-12 through Reserve and north to the Eagle Peak road, where we tum east. Stop I is in the deepest part of the Reserve graben, along the Tularosa River north of Reserve, where we will discuss the evolution of the graben structure, sedimentology of the Gila Formation (Oligocene to Pliocene), and the local volcanic stratigraphy. Stop IA, nearby, provides an opportunity to see a basalt flow interlayered in the Gila Formation and to examine a small reverse fault that is related to a small-scale buttress unconformity.

Upon returning to NM- I 2, we continue north to Apache Creek, where we take NM-32 northwest for about 9 mi to Stop 2, where relatively new roadcuts expose volcaniclastic sediments of the Spears Group (Eocene and Oligocene) beneath andesite lava flows of Dry Leggett Canyon (~34 Ma). Here we discuss the provenance and sedimentary structures in this sequence of well-sorted sandstones, the origin of numerous, thin, pink ash-beds interlayered with the sandstones, and the origin of the black fiamme and the pink, bedded deposits in which they occur, between andesite flows.

After we return to Apache Creek, we continue east on NM-12 to Old Horse Springs, Stop 3. At this stop, we examine pyroclastic deposits at the eruptive center of the Horse Springs dacite (informal unit), and mineralized jasperoid inclusions ( sil icified pre-Tertiary limestone, quartzite and argillaceous rocks), with skam-type reaction rims. From this vantage point, we can also discuss the structure of the San Agustin half graben as revealed by seismic profiles, the small hogback of preTertiary rocks (Laramide high?) at the foot of the Horse Mountain volcano on the northern margin of the graben, the alignment of Bearwallow Mountain volcanoes on its southern margin, and the results of the recent oil play in this region.

Stop 4 is at the small hogback of Permian sedimentary rocks at the base of Horse Mountain on the north side of NM-12 about 6 mi east of Old Horse Springs. This is an optional stop'. and there may not be sufficient time on this field trip to examine these outcrops that are believed to represent the Mogollon Rim, a relict of the Laramide uplift at the southeast margin of the Colorado Plateau in this area. Tertiary stratigraphic nomenclature used in this third-day road log follows the proposals of Cather et al. (this volume).