There were two EVAs today with geology as their primary purpose. Our goal for today was to get below the level of the Hab in the geologic section, as I suggested yesterday, and to see what we could find.

The morning EVA was Binsted and Childress, who headed south along Lowell Highway to visit White Rock Canyon. Since neither of these two is a geologist, I think the experience was very interesting for them as well as for me. I tried to give them fairly detailed objectives before they left and also instructed them to use their judgment to collect samples of interest. Since they were the ones doing it, I think they felt more engaged by the geology. And it was interesting for me back at the Hab to listen to their EVA check-ins and local radio traffic about rocks, and then to anticipate what they were bringing back. We had a good debrief right after they returned about what they saw, and they talked me through some sketches they had made and gave me the GPS coordinates of their samples.

The afternoon EVA was O'Connor and me. We headed up onto the Hab Ridge level and then further west to join the main north-south road. After heading north for a kilometer or so we were well into the Lower Blue Hills area, with mounds of blue/grey clay to traverse. Although these hills probably originate due to surface erosion, in several places they give the appearance of a dune field. Although I did not notice any small-scale rippling on the surface, as you would see with sand, the tops of some hills/dunes were corniced. Eventually we struck the turnoff down into the northeast trending wash that leads to Muddy Creek. We followed this wash all the way to the creek and explored there on foot for some time.

There were large amounts of stream-deposited materials, sand- to boulder-sized, with a mixture of lithologies, but the in situ rock along Muddy Creek is a clean white sandstone. This layer was slightly cross-bedded and approximately 10 meters thick. I was especially pleased to see this layer because it appeared to match perfectly with some samples of sandstone returned by the morning EVA crew from the appropriately named White Rock Canyon far to the south. Although lithologies repeat in the sequence in this study area, making casual correlation uncertain, it seems plausible that we have looked through two windows and seen the same view, so to speak. Both of these exposures are at about the 4400 foot index contour level on the Skyline Rim topo map.

At this point I'm reminded of a clean white sandstone that we found during EVA 5 cropping out at the cliff top just north of the north end of the Lowell Highway as it is shown on the map. At the time I hypothesized that this layer was equivalent to the Observatory Hill sandstone, but I now think it is more likely to be the same as what we've found today on our two EVAs because of its nature and because it is also near 4400 feet in elevation. But what is this layer? The Salt Wash member of the Morrison? Or the Tidwell? I think it is likely to be one of these, with the siltstones of the Summerville underlying it, but I am not sure. More work would be needed to place this and the numerous vari-colored shales above and below into context. For example, Binsted and Childress reported maroon and greenish clay layers just below this white sandstone, but see below.

As a last note, each EVA team found an unusual rock today. The southern EVA team returned with what appears to be a porphyritic andesite, pulled from the alluvium in the wash above White Rock Canyon. Although we have found several locations with igneous boulders, these have been uniformly vesicicular basalt up till now. All of these have evidently been brought in from the south and west(?), showing the effects of surface water. But we have not yet found any perched high enough to serve as good evidence for previous floods, as we have sought. (Consider the situation just west around Capitol Reef, where basalt boulders litter many high areas as well as the washes.)

O'Connor and I found the other odd rock while returning up the wash from Muddy Creek on this afternoon's EVA to the north. Leaving the rovers, we walked up a winding slot canyon to the south, where we found a beautiful specimen of green sandstone, with sections of well-developed desert varnish. It was not rounded, and the desert varnish was in many places intact, so it could not have traveled far down the wash, but the sides were red clay up as far as you could clearly see. Well up the canyon sides were some thin layers of maroon and green/grey clays, much as the morning's EVA team described, but we were puzzled as to where this sample could have originated. After returning to the ATVs and heading up the wash to the southwest, we saw on the south side a bit more of the green sandstone, trailing down from a thin layer in the canyon wall. What we thought was green clay high on the walls of the canyon where we found the green sandstone must have been in fact green sandstone. Obvious in hindsight, I suppose, the fact that the morning's EVA team described green clay must have prejudiced us. I've seen this lithology nowhere else. It is up-section of the white sandstone I discussed earlier, and I will report the UTM coordinates of our initial find tomorrow after reviewing notes. But the maroon and green layers above and below the white sandstone just point out the problems with casual correlation in an area of repeating rock types.