Geology work over the past two days has been a mixture of revisiting the Lith Canyon area for further observations and "exploration geology", whereby we have expanded our area of investigation up onto the level above Hab Ridge. Having spent several days' EVAs investigating exposures of the Dakota Sandstone and the underlying Observatory Hill sandstone layer, we have decided to go up and down section into the Mancos Shale and the Morrison Formation. Of course, these layers are typically thick shales, eroding into broad slopes and rolling plains, and they only give good opportunities for seeing them in cross-section just under overlying sandstone caps. However, before leaving a discussion of the Dakota Sandstone, I have one final observation/question about this interesting unit.

I've passed through or looked at the hills that make up Bob's Rock Garden numerous times in the past week or so -- a curving line of hills extending east from the Hab Ridge level, and capped (though just barely so) with Dakota Sandstone. In fact nearly all of the sandstone (cross-bedded and conglomeritic) has tumbled off the tops of these hills, and you have to dodge through it while driving in or out on the Lowell Highway. But I never noticed until today that by far the majority of these sandstone blocks lie on the north-facing flanks of these hills. Why? Well, two ideas come to mind, and I want to share them both and request comment from anyone who would like to respond.

First, this line of hills trends slightly north of east. Is this slight northward orientation enough so that the westward dip, gentle though it is, encourages boulders to tumble off the north (and slightly west) sides. Perhaps sapping of the shales just beneath the sandstone due to rainwater percolating through the former sandstone caps and traveling down-dip (west) on top of the shales caused the cap to be undermined more on the northwest side. Second, is it possible that the north-facing slopes weathered more due to the slightly colder temps and slightly greater moisture content that north-facing slopes typically have? I have seen this second phenomenon manifest itself as much steeper north-facing slopes, compared to south-facing ones, in humid climates. But, I'm not sure how it would manifest itself here in an arid climate, and the north-facing slopes don't appear to be steeper, neither by observation nor on the topo map. Comments?

In reference to our EVA today onto the Hab Ridge level, I'll only say at this time that we were going primarily to scope out the best, nearest routes up there. We traveled north up the Lowell Highway, and then we turned west beyond Tank Wash, at about 4254500 N on the road. The path (for road is too grand a name) leads gently upward over generally grey hills of clay so that the attainment of the Hab Ridge level goes unnoticed. I think this route would be a sore trial in wet conditions, but it is perfectly passable when dry. The web of ill-defined routes and will-o'-the-wisp tracks allows you to have a choice among doubtful roads, but the fact that the Skyline Rim looms to the west keeps you well-oriented. As you head south and somewhat east, the plain becomes more sandy and rises. The lip of Hab Ridge defines itself, and you know you are getting close when you pass into gentle hills littered, sometimes paved, with fossil oyster shells. We continued along a defined trail that parallels Hab Ridge until we were nearly as far south as the Hab. After admiring the view over the Hab eastward, we returned north a short distance to a point where a distinct roadbed, somewhat graded, turns east over the lip of Hab Ridge. (This roadhead is near 518000 E and 4251300 N.) This road descends to the level of the Hab along the south side of the saddle between Hab Ridge and the hill visible from the window over the kitchen sink. Although the road is graded on the descent, there is a place or two where erosions threatens it and care should be taken. It is generally in the red rather than in the grey clay, but I still suggest this as a dry road only. Also, it is worth nothing that while this roadway is obvious from the top but not from the bottom. We hope to build a small cairn to mark the lower approach.

With a quick route up to the Hab Ridge level, we look forward to visiting the Skyline Rim, and we want to see and collect from the Ferron Sandstone. We'd also like to work north on the Hab Ridge level to the greatly dissected north end, where both the Hab Ridge and the Hab levels seem to merge.