Precision In Situ Field Geologic Contact Mapping by MERA, Columbia Hills, Mars

The positions of identified lithologic contacts, outcrops, traverse landforms, and data derived from in situ measurements of outcrop materials by the Athena instrument suite have been determined by stereo-ranging and rover tracking along the traverse by MERA (Spirit) within the Columbia Hills. High precision geologic maps of several sites and moderate precision transect maps between sites have been constructed fro these data showing the geology of Spirit's path through the Columbia Hills. The overall accuracy of contact locations with respect to global position reflects the overall accuracy of knowledge about the rover location. But measurements of contacts from multiple (as many as five) positions agree remarkably well and are well within the standards and limitations acceptable within terrestrial field geologic contact mapping precision. Orthographic maps of the results along the traverse also agree well with features in narrow angle MOC images crossed during the traverse. Some site-to-site variations in lithology and chemistry within the Columbia Hills reflect possible variations in surficial materials. But other differences between outcrops could be a result of variations in alteration of a limited range of protoliths draped as either distal crater ejecta or volcanic air fall materials over a Columbia Hills substrate. Large scale changes in lithology along the traverse, and particularly abrupt discontinuities coincident with through-going linear trends are evidence for possible structural (faulting) control on exposures that expose fundamental differences in basement or substrate materials. The geological complexity of the Columbia Hills appears comparable to that of some ancient continental basement terrains.