In contrast to yesterday's efforts in terms of geology, where we were trying to look beneath the landscape visible from the Hab by visiting canyons on the north and south end of this area, today we were trying to look above this level, up-section into the Mancos Shale, into younger rocks. Therefore, our morning EVA set out with these goals: to observe the Skyline Rim from its base and to collect samples of the Ferron Sandstone, if possible, from blocks that were expected to litter the slopes below.

We were successful in both of these goals. The Skyline Rim is a short ATV trip to the west once you have climbed up onto the Hab Ridge level, with only about 2 kilometers separating Hab Ridge and the Skyline Rim at this point. Starting just 10 meters or so west of the top of Hab Ridge you drive across a broad scattering of oyster fossils, often so thick as to seem like gravel on a gravel road. As you travel slightly farther west pebbles begin to make up a large part of this litter. I have wondered for several days whether these oysters have weathered out of the top of the Dakota Sandstone or whether they have weathered out of the lowest (and now absent) layers of the Mancos Shale and have simply collected on top of the underlying Dakota. Regardless, this oyster layer seems the best indicator of the contact between the Dakota and the Mancos, a contact difficult to locate with any specificity on the Hab Ridge level and in the wash on the north end of this level, which leads down to Muddy Creek.

At the base of Skyline Rim we stood admiring the cliffs above. While it is difficult to estimate height, the topo map shows the change in elevation at about 400 feet, counting the height of the fans at the cliff's base. The cliff is capped with a relatively thin layer of clean, yellow sandstone. Some blocks of this near the base of the cliff allowed us to collect samples. Below this cap, there is an equally thick slope, which indicates a shaly member. Below this is a relatively thick layer of what appears to be a thinly bedded light and dark sedimentary rock. Samples, presumably from this rock unit, collected at the base of the cliff are red and fine grained, essentially silty. All of this appears horizontal in north-south cross-section, but probably dips gently to the west. A question that posed itself to me was why are there so few blocks of the Ferron Sandstone on the level of Hab Ridge, even near the base of this cliff. Even with a slow rate of retreat, you would think there would be quite a litter of these blocks, especially since there is no large wash below to remove the boulders. Instead, piles of grey clay begin right at the base of the cliff. Comments?

With these samples stowed away, we returned to the east, pausing briefly at the top of Hab Ridge where the road/trail down begins, to investigate the oysters and the sandstone. There we found some oysters shells still in the sandstone, which appears to answer the above question about these oysters (an answer probably hinted at by the fact that oysters are filter feeders).

I spent this afternoon sorting samples and arranging them for display, and also in noting the locations of these samples on the topo map. I've created a display to show the other crew members and the visiting media tomorrow, if they are interested. It is interesting to me how many samples of sandstones we have and how few of clay, which is not really representative of what you see in this area.