Second-day road log from Las Cruces to Selden Canyon, Broad Canyon, and Rincon Arroyo
— Greg H. Mack and Nancy J. McMillan

The second day of the field conference is dedicated to the Cenozoic history of southern New Mexico exposed in Selden Canyon, Broad Canyon, and near Rincon. The first stop in Selden Canyon is a roadcut of the late Eocene Palm Park Formation, which consists of very coarse-grained andesitic lahars. The Palm Park Formation represents volcanism that immediately preceded the onset of crustal extension of the Rio Grande rift and post-dated Laramide shortening. The second stop is a long traverse up Broad Canyon to examine Oligocene and Miocene rocks that formed during the early evolution of the Rio Grande rift. Stratigraphic units encountered include the early Oligocene Bell Top Formation, the late Oligocene Uvas Basaltic Andesite (including part of a cinder cone), and the late Miocene Rincon Valley Formation, including the 9.6 Ma Selden Basalt. These rocks are exposed in the Cedar Hills transfer zone, which is between the west Robledo Mountains fault and the Ward Tank fault (Mack and Seager, 1995). Two of the normal faults within the transfer zone can be observed on the traverse. The Broad Canyon traverse ends with a view of Native American petroglyphs etched into ash-flow tuff 5 of the Bell Top Formation (Seager et al., 1975). The third stop is in a tributary canyon to Rincon Arroyo, where the axial-fluvial lithofacies of the Plio-Pleistocene Camp Rice Formation is exposed beneath the La Mesa geomorphic surface. Important features at this stop include the stage V petrocalcic paleosol beneath the La Mesa surface (Gile et al., 1981), calcic paleosols within the Camp Rice Formation (Mack and James, 1992), and a pumice-clast conglomerate within the Camp Rice Formation derived from the lower Bandelier eruption in the Jemez volcanic field (Mack et al., 1996). In addition, age dating and correlation of the Camp Rice Formation using reversal magnetostratigraphy will be discussed (Mack et al., 1993).