The Colorado Geological Survey (CGS) completed a multi-year field investigation of the Anton escarpment on Colorado’s eastern plains to determine if this linear, 135-km-long, 24-m-high feature is seismogenic in origin. We dug 600 meters of trenches augmented by borehole cores and a seismic refraction survey. Sediment samples were dated using luminescence and radiocarbon techniques. We used a high-resolution stratigraphic framework to evaluate the nature of geomorphic evolution on and adjacent to the escarpment. We found no evidence of faulting. The trenches exposed a succession of predominantly eolian units overlying gravels of the Miocene Ogallala Group. The upper escarpment contains late Pleistocene sand dune (70 to 38 ka) and loess and sand sheet (29 to 16 ka) sediments. The flanking low area is floored by eolian loess and sand layers (Pliocene to middle Pleistocene) with strong calcic paleosols. These are overlain by a zone of polygonal sand wedges and other periglacial features (27.5 to 16.5 ka), sand sheet and playa deposits (16.5 to 12.5 ka), and loess with humic paleosols (12.5 to 6.4 ka). The younger (post-29 ka) units form discontinuous sediment bodies that overlie gullied, bowl-like, or flat-bottomed erosion surfaces with up to 27 m of paleotopography. The older units appear to be continuous beneath the escarpment face. We interpret that the Anton escarpment is not a late Quaternary paleoseismic feature, but instead was created by paleowinds. It marks a linear interface between an extensive, late-Pleistocene plateau of thick loess and sand deposits dominated by eolian aggradation and a contemporaneous, adjacent, topographically low plain dominated by wind erosion and partial infill.
Hillshaded DEM of eastern Colorado showing the Anton escarpment (white arrows), about 160 km east of Denver, Colorado.
Click here to view the FINAL REPORT on the Anton Escarpment
Click here to view the UPPER TRENCH LOG
Click here to view the LOWER TRENCH LOG
Click here to view the PLAYA TRENCH LOG
Click here to view the CENTER TRENCH LOG