First-Day Road Log: Mesa Portales And The Sierra Nacimiento Front Via Arroyo Chijuilla, The Piedra Lumbre Road, And San Miguelito Canyon
— Kevin M. Hobbs, Jerry Kendall, Susan Lucas Kamat, K. Luke Martin, and Amanda Cantrell

Day 1 of the field conference travels a counter-clockwise loop around Mesa de Cuba and Mesa Portales, the two stratigraphically highest of several sandstone-capped mesas marking the southern edge of the San Juan Basin near Cuba.
Most of the drive is through regions of sedimentary rocks deposited at or near sea level in the Western Cordillera from the Mesozoic through the early Cenozoic. Now higher than 2 km (1.2 mi) above sea level, these sediments record a fascinating tale of tectonic evolution of the western part of our continent. Subsidence that accommodated sediment deposition was facilitated by a combination of crustal processes that we discuss throughout the day. Uplifts during the compression- dominated depositional history of these rocks provided a sediment source, but also led to unconformities that we discuss at Stops 2 and 3. The late Cenozoic uplift of the Colorado Plateau leads to today’s high elevation, but tensional tectonics relating to the Rio Grande rift—just a few kilometers to our east—now changes the landscape. A unifying question for each of today’s stops is “What can sedimentary rocks tell us about the tectonic history of a region?”.