New Mexico Geological Society Annual Spring Meeting — Abstracts

The Rio Cebolla drainage basin is a relatively large basin (area=120 km²) located in the western part of the Jemez Mountains of northern New Mexico, between the Valles Caldera to the east, and the Sierra Nacimiento to the west. This research focuses on the characterization of the spatial and temporal variations in the geomorphology, sedimentary deposits, and associated soils in the two main forks of the Rio Cebolla drainage basin: Calaveras Canyon and the upper Rio Cebolla drainage basin. These tributary basins are both underlain by the Bandelier Tuff and are nearly identical in drainage area, orientation, elevation, and vegetation type and due to the close proximity of the basins (trunk streams are only about 1.5 km apart) it is reasonable to assume that they have been subject to the same climate and climate changes. The drainage patterns and other important geomorphic features of the basins' valley bottoms, however, are markedly different. Calaveras Canyon contains at least 2 preserved stream terraces and has a well-developed dendritic drainage pattern, while the upper Rio Cebolla basin contains no preserved terrace remnants and has a much more linear drainage pattern with limited tributary branching. In addition to differences between basins, the geomorphic features also vary within the valley bottom of Calaveras Canyon. The valley bottom of the ephemeral portion of Calaveras Canyon contains two distinct, laterally continuous geomorphic surfaces. The upper surface is a fluvial terrace, located approximately 2.5 meters above the channel bed, and the lower surface is the current floodplain, located about 0.5 meters above the channel bed. Bar-and-swale topography and many surface boulders characterize the modem floodplain in this portion of the canyon. In contrast, the floodplain in the portion of Calaveras Canyon fed by perennial springs lacks bar-and-swale topography and is underlain by finer-grained deposits; also the 2.5-meter terrace is not preserved in this portion of the canyon. Dendrochronological methods have been implemented in order to assign minimum ages of relative stability to the surfaces present in Calaveras Canyon. Preliminary data indicate a minimum age of 500 years for the 2.5-meter terrace and 130 years for the modem floodplain.