1st Trip: On 2/10/2012, Rod Horrocks led Everett Brill to W.C.T.U. Hall in the Historic Section to study the stream cobbles for his Senior Geology research project.
Trip Report: I took Everett Brill, a SDSM&T geology student, to W.C.T.U. Hall on the Garden of Eden Tour Route to begin work on his Senior Geology Thesis project studying the five known cobble sites in Wind Cave. We decided to start with the most easily accessible site first, just in case our initial work found that we had to return to the site a second time. This proved to be a wise decision. We found two deposits of cobbles in the room, one in the NW corner of the room and another in a small passage underneath Silent Lake. The two are obviously related and resulted from the same flood event. We theorized that the source of the cobbles might have been from the dome above Silent Lake. Crawling into the site underneath Silent Lake, we characterized 100 cobbles. Although, we found that much of the site had been disturbed when it was surveyed, some deposits were still untouched. There was also a large calcified siderite concretion that was broken in half and some concrete on it right at the entrance to the crawl.
The task of characterizing the cobbles was made more difficult due to numerous pieces of paleofill and associated rubble that had fallen off the roof and got mixed in with the cobbles. We found that most of the cobbles were either white sandstone, light colored sandstone, dark quartzite, quartz, or limestone. We also noted that most of the cobbles at this site were 64mm or smaller with only a couple almost 128mm.
We then went over to look at the other site in the NW corner of W.C.T.U. Hall. We found a complete silicified siderite concretion sitting at the entrance to a side passage I had never noticed before. The size of that concretion tells us that the old paleo entrance was pretty good sized to allow a 2 ½ foot concretion to wash down it. Looking into the crawl, we saw extensive cobble deposits and an area that I'll have to return and survey. The plan is to return next Friday to map the deposits.