Second-day Road Log: From Circle A Ranch to La Jara, Regina, Llaves, and Deadman Peak; Returning Through Canoncito De Las Lleguas, Canada Simon, and The Upper San Jose Valley
— Kevin M. Hobbs, Shari A. Kelley, Thomas Valenzuela, and Brian Hampton

Day 2 of the field conference travels north from Cuba along the eastern margin of the San Juan Basin. From Cuba to Regina, the Sierra Nacimiento, the basin-bounding uplift to the east, stands with over a kilometer of relief over the adjacent basin. Its uplift occurred along the Nacimiento fault. North of Regina, the uplift occurred partly along faults, but also along the broad Archuleta/Gallina anticlinorium. This complex of domes, faults, and anticlines exposes kilometers-long cuestas of classic Western Interior Seaway stratigraphy, including one that is the focus of our Stop 1. Some of the basin-bounding faults at the northern end of our journey today have normal offset—the opposite of what is expected in Laramidia. Stop 2, near Deadman Peak and overlooking the structurally spectacular Rio Gallina Canyon, puts these into context with recent mapping and structural interpretation. A short drive down Deadman Peak brings us to Stop 3, where we investigate the Greenhorn Limestone, one of the few carbonates from the Western Interior Seaway in New Mexico. There, we discuss why the Cretaceous in much of western North America lacks the rock types (carbonates) for which the Cretaceous is named. From there, we travel upsection into the basin through Cañoncito de las Lleguas (Little Canyon of the Mares) through unsurpassed sandstone outcrops of the San Jose Formation. At Stop 4 in Cañada Simon, we get the latest on tectonics, sedimentology, and geochronology as interpreted through a modern investigation of the San Jose Formation. Returning to the south, an
optional stop (Stop 5) overlooking the Llaves Valley allows us to consider the neotectonic development of the region. Throughout the day, we consider the timing, sequence, and impacts of geologic events that culminated in the modern San Juan Basin. We also challenge previously held assumptions about how the San Juan Basin has been, is, and should be defined.