Another good week in the field! Continued fairly dry fall weather means we’re still in the big drainages this week. Finished up in Weaver Creek on Monday. Still have the channel-bedded mostly shaly unit in the valley and the thin- to very thick-bedded sandstone unit on the southeast side of the valley. Got to see the thickness of the alluvial cover in the high wall of a shale pit in the middle of the valley. The owner states that the pit is 60 feet deep and is shaly to the bottom. That’s a lot of shale! The sandstone above it is at least that thick and probably more like 100 feet. Still seeing channel beds within the sandstone unit as well. A ribbon snake crossed our path heading toward the water.
The next day, we tried to cross the Middle Fork as we have done in past weeks, but there is already too much water in it. There are some deep hollows on the east side that we needed to get to, but after fording the river proved impracticable, we resigned to going north on highway 9 and dropping off the top edge of the valley. At least we started from the lowest saddle. It was a fairly easy descent with a few washed out 4-wheeler trails helping out. We knew right away we were in Witts Springs when we reached the bottom, but were surprised by how low the contact was when we reached the Cane Hill. When we reached the river valley, we decided to follow a slough upstream to the next drainage on the east side. This looked like the best route on the map, but was actually a thick canebrake with very few places to cross the slough. We had a hard time getting in the upper end of this drainage a few weeks ago, and the lower end proved no different. We were rewarded by finding a lot of deformation bands along non-vertical joints in the Witts Springs, and a drop of about a hundred feet in the contact with the Cane Hill between the drainages, which are only separated by about a mile. At best may be a monocline in there. On the way out we nearly ran over what I hope is the last moccasin of the season sunning on a very steep hillside above the drainage. We gave him as wide a berth as we could and continued back to the river bottom. This time we tried to avoid the slough and stayed closer to the river where the switch cane was thinner. We backtracked up the hollow we came down earlier, then climbed back up the side to the highway. So to summarize, river unfordable so drove around, hiked down 420 feet, bushwhacked a mile through canebrake, hiked up 320 feet, saw deformation bands, back down 320 feet, avoided snake, hiked a mile through woods, climbed back up 420 feet. What a day!
On Wednesday we started on the west side of the river downstream of where we were the day before, and walked up one of two remaining large drainages before the river turns northeast at Shirley to follow the lineament. We were rather surprised to find Imo near the mouth of the hollow. This would make it the southernmost exposure of Imo mapped to date. Saw good exposures of Cane Hill, which is mostly sandy through here, on the way to a classic example of the basal Witts Springs sandstone complete with exfoliation weathering.
Once we got out of there, it was back to Little Rock and back to reality.
Oh, and I almost forgot. I found this graph on the USGS website and thought you might find it interesting. You can see that flood event on the last day of May this year that we are still seeing evidence of. Apparently it was right up there with some of the biggest recorded events on the Middle Fork in that area.
Looks like we’ll be in the office next week, so next installment in two. Until then, I’ll see you on the outcrop!
Tick attacks: very light
Snake count: 2