Second-day Road Log: Chupadera Mountains
— Daniel J. Koning, Richard Chamberlin, and David W. Love

Today we study the stratigraphy and structure of the eastern face of Socorro Peak, also known as “M Mountain,” a landmark ingrained into the spatial consciousness of folks living in Socorro, before delving into the Oligocene-Miocene volcanic and sedimentary rocks seen in the Chupadera Mountains to the south. There is a lot of geology to see on the eastern face of Socorro Peak, and it provides a nice preview of Oligocene- Miocene volcanic and sedimentary rocks that we will later observe in the Chupadera Mountains. Both Socorro Peak and the Chupadera Mountains provide important clues on the volcanism and faulting that occurred during and after the formation of the Socorro caldera, which formed in a cataclysmic eruption at 32.35 Ma that expelled the widespread Hells Mesa Tuff. Geologic maps and precise age determinations from the NM Bureau of Geology Geochronology Research Lab provide evidence for a complex volcanic, sedimentary, and structural history for the Socorro caldera and the Chupadera Mountains. Note that all ⁴⁰Ar/³⁹Ar ages presented here are based on a sanidine (FCT) monitor age of 28.201 Ma (Kuiper et al., 2008).