New Mexico Geological Society Annual Spring Meeting — Abstracts

Under a newly funded EDMAP Data Synthesis Project, we are working to produce a 1:24,000-scale digital geologic map of the San Ysidro Quadrangle in north-central New Mexico. This quadrangle is at the geologic nexus between the Colorado Plateau, Southern Rocky Mountains, and Rio Grande rift. Recent focus on this area during the New Mexico Geological Society 2024 Fall Field Conference highlights its new research and mapping importance. This project will synthesize 1930-1980s legacy mapping with new mapping, neotectonics, geochronology, and tectonic geomorphology studies. The mapping project is complementary with ongoing mapping of the New Mexico STATEMAP program and the USGS Earthquake Hazards Program. This project represents the first integrated surficial and bedrock mapping at this scale for the iconic San Ysidro area since the 1976 Woodward and Reutschilling map.

The mapping effort aims to answer questions about the extent and magnitude of Quaternary fault reactivation of Laramide and rift structures leading to a new understanding of fault segmentation on the margins of the Colorado Plateau and Rio Grande rift. We employ studies of river incision rates across proposed faults, as recorded by terrace flights with timing constrained by new detrital sanidine and luminescence (IRSL) geochronology to estimate differential rates across major structures. The mapping uses recently updated stratigraphic nomenclature for Paleozoic and Mesozoic strata and advances in Proterozoic geochronology to update bedrock geology of the quad. 1m lidar and aerial digital mapping enhance map accuracy and rectify multiple generations of mapping within the area. Outreach involves renewed UNM/NMBGMR interaction with the Pueblos of Jemez and Zia whose ancestral lands are within this and adjoining quadrangles. Geo-cultural engagement is guided by the understanding of this area as an interwoven cultural and geologic nexus and complimentary with place-based education efforts at UNM. This map synthesis fills a timely gap at the nexus of the margins of the San Juan basin, Rio Grande rift, and Southern Rocky Mountains amid a new generation of research to understand the margins of the Colorado Plateau and rift.