Today was a great day for geology, with beautiful weather and almost unlimited visibility. We took advantage of this opportunity to get out and about by going on an extended EVA north of the HAB. We traveled by ATVs and drove to the north end of Cow Dung Road. Our goals were to investigate and sample several locations where we believed we could see the Dakota Sandstone, based on study of the Skyline Rim topo map. It appears that 4,600 feet, in the notation of the topo map, marks a good target elevation for finding this formation in the area around the HAB. Also, we hoped to use the mobility of the ATVs to let us see much of the landscape in this area, and, of course, we were looking for other interesting samples to collect.

This was a successful EVA in all ways. Geologically, we did find that all of our target hills were capped by sandstone, presumably the Dakota. This sandstone was generally yellow to brown, coarse grained, and typically conglomeritic. It was also cross-bedded in some areas. A big brown cap on top of the hills that rise above the red and grey Morrison is a sure sign of this formation. The hills we investigated lie 1) north of the hab by about 1 km, on the west side of the dirt road (this hill is visible from the window over the Hab's kitchen sink), 2) well north along the road, after the road turns northeast (marked 4614 on the topo map), and 3) at the end of the road as it appears on the map. (This road actually continues over the hill to the northeast, stopping at a cliff which overlooks Muddy Creek.) Our sampling was successful, and the samples need a bit of comparison in the laboratory tomorrow with those collected on the EVAs of 3/20.

At the end of Cow Dung Road, slightly beyond where it appears to end on the map, there is an exposure of white or light grey sandstone, all along the rim of the cliffs on the near (west) side of Muddy Creek. This layer, lower in the sequence than the Dakota, was bare and smooth. We took a sample of this, too. By looking at the nearly vertical NE side of the hills where the road ends on the topo, we could see that this white layer is separated from the overlying Dakota by a thickness of red (on the bottom) and grey shales. Although this lower sandstone unit is not crossbedded, or not obviously so, and although is white rather than yellow, I believe it is the same relatively thin sandstone layer that makes up Observatory Hill, where the telescope is. This is the layer I commented on in my last geology report, asking whether it is a member of the Morrison, which today's observations make me more inclined to believe. Comments from anyone on this?

Near this white sandstone we also found numerous boulders of vesicular basalt, at least by field observation. The largest of these were approximately 12-16 inches in diameter. One of our goals, as noted before, is to find these boulders perched high in this area, out of present-day washes, in order to support the hypothesis that these boulders were transported into this area from the west (or possibly south) during times of past abundant surface water. However, although relatively high (fairly near the top of the Morrison, a bit less than 4,600 feet), these that we found today were in a small drainage near the lip of the cliffs over Muddy Creek. Although this drainage is not large or long, still it is a drainage, and therefore these boulders are not the sort of evidence we wanted. We'll continue looking.

A last note: On our return the sun was in the southwest, and numerous mineral samples lying on the surface of low hills of the Morrison sparkled brightly in the sun. We investigated and found that the sparkles were from cleavage surfaces on bladed minerals. A quick check on our return to the HAB showed these samples to be gypsum.

Tomorrow we plan to extend our investigations to some of the units above and/or below the Dakota, probably by following drainages up or down from Cow Dung Road. Any suggestions from anyone out there would be welcome.