Exposure of relict high level gravels sampled during EVA-31.

EVA-31 on February 26th visisted the residual gravels on the ridge near where Cow Dung Road meets the fence line to the west of White Rock Canyon. These gravels had been observed on EVA-12 to contain a diversity of igneous lithologies. While not in situ, such an assemblage can still provide information on the range of igneous rocks in the source area of the gravels. In the case of these deposits, the gravels could either have been derived from areas to the west of Capitol Reef and transported by an ancestral stream to the Freeont River, or they could have been shed into alluvial fans by the exposure of the igneous rocks of the Henry Mts.

Relating the composition of the rocks in the gravels to the known rocks in the possible source areas will allow those source areas to be identified. On Mars, sampling such gravels would similarly allow understanding of the geology source area which may lie outside the area which can be explored by the mission. The Mars Pathfinder landing site was selected for such a reason, as it was believed that catastrophic flooding had transported a range of lithologies to the site.

On this EVA Melissa Battler and Rocky Persaud collected about 10 different intrusive igneous rocks and 8 different volcanic lithologies. Intrusive rocks were typically felsic to intermediate with large feldspar phenocrysts and many had large hornblende crystals and the volcanic rocks were more basically and typically vesicular with the flattened vesicles up to 8 mm in length. These samples will be forwarded to Stacy Sklar at Northern Arizona University for further analysis at the end of Expedition One.