GEOMORPHOLOGIC DESCRIPTION AND CATEGORIZATION OF SOD TABLES IN BADLANDS NATIONAL PARK, SOUTH DAKOTA

The sod tables of the White River Badlands of South Dakota exist as remnants of Quaternary alluvial-colluvial fans deposited during the erosion of the adjacent ‘castles’ of the Tertiary Brule and Sharps formations. Using surveying techniques during field mapping, we determined that at least four levels of sod tables can be mapped as stepped surfaces ranging in height from 0.5 to 10 m above channel bottom in adjacent washes. Sod Table One (ST1) is about 0.5 m high, ST2 is at 1.3 m, ST3 is at 3 m, and ST4 is at 5 m. Evidence suggests another surface, ST5, is rarely observed at about 10 m above adjacent active channels. Mapping was completed in an area paralleling the major escarpment (which runs nearly E-W) for a distance of about eight kilometers and within about one kilometer both north (above) and south (below) of the cliff band. Resolution of large 1:10,000 aerial photos was sufficient to discriminate most sod tables and to record their attributes upon overlays. These data will be entered into a GIS package to query additional spatial relationships regarding proximity to the escarpment. Difficulties encountered in discriminating between sod table levels include (1) some tables appear to be sourced from adjacent higher tables, in contrast to being sourced from Tertiary ‘castles’, (2) selection of the principle channel within a catchment to base vertical measurement and sod table numbering upon can be tricky due to the obstructed views of the rugged topography, and (3) individual sod tables can be observed to undulate or sag abruptly in a fashion conflicting with the anticipated original depositional grade, typically existing on these fans. These difficulties suggest that additional study involving stratigraphic correlation and the use of various dating methods would assist in categorizing individual tables. We postulate that the sod tables that exist at various distinct levels may reflect multiple generations of alluvial-colluvial fan development. This assertion would further imply that the balance between sediment supply delivered from the ‘castles’ and its removal has varied to produce periods of net aggradation and the building of fans, from periods of net degradation, incising into and producing fan remnants, which exist as sod tables today. Changing paleoclimate may have driven this dynamicism, but such remains conjecture.