HYPOTHESIS TESTING FOR THE ORIGIN OF CRATER-LIKE FEATURES NEAR GREAT SAND DUNES, COLORADO

For decades, residents of Crestone, Colorado have pondered the origin of a ~100 m diameter crater-like feature south of their town. The primary theory suggested a small meteorite impact formed the feature, but geological and geophysical surveys have yielded no conclusive evidence of an impactor or other signatures of a collision sufficient to produce a crater of the observed scale. Recent airborne laser altimetry surveys have produced high-resolution digital terrain models of the San Luis Valley. Shaded relief maps of these DTM’s revealed similar crater-like features distributed over a unique unit of eolian sand. Mapping these features shows spatial correlation with the maximum estimated shoreline elevation for Pleistocene Lake Alamosa, suggesting the paleolake’s hydrology played a role in their formation. Evidence of Pleistocene alpine glaciation is also found upslope of this unit of crater-like features, suggesting a paleoclimate that was cold and wet enough to support periglacial activity at relatively low elevations (<2500 m). Quaternary lakeshore processes, the eolian sediments in the valley, and climate change could have all played a role in the formation of these geomorphic features. We define tests for the hypotheses of extraterrestrial, eolian, or periglacial origin such as geologic setting, rim/depression geometry, spatial density, mineralogy, and subsurface structure. These tests are applied to previously acquired geological data and considered in recommendations for future remote, field, and/or lab studies. Understanding the origin of these crater-like features may have implications for the ongoing study of spatiotemporal evolution of surface processes on both Earth and Mars.