• Wind Cave National Park - Two Worlds

    Wind Cave

    National Park South Dakota

Stream Cobble Study

Rod Horrocks recording survey data in Cobble Hall

Rod Horrocks recording survey data in Cobble Hall

NPS Photo

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.

 

2nd Trip: On 2/17/2012, Rod Horrocks led Everett Brill to Cobblestone Crawl in the Historic Section to study the stream cobbles for his research project.

Trip Report: I took Everett Brill, SDSM&T Geology student, to Cobblestone Crawl to look at another cobble site for his Senior Research Project. It was immediately obvious that the cobbles in Cobblestone Crawl area are related to the cobbles in W.C.T.U. Hall. The composition of the cobbles were the same, however, they were generally smaller and more rounded than the cobbles in the W.C.T.U. Hall area. We assume this means that Cobblesteone Crawl is farther from the paleo entrance or source of the cobbles, while W.C.T.U. Hall cobble area is closer. After characterizing 100 cobbles, which we accomplished in half the time that it took us the previous Friday, we mapped out the cobble deposit and called it a day.

 

3rd Trip: On 2/18/2012, Rod Horrocks led Kenny Slocum to W.C.T.U. Hall in the Historic Section to survey the Cobble Maze area.

Trip Report: We went to W.C.T.U. Hall to survey a lead I had spotted the previous week when looking at the stream cobbles in the crawl underneath Silent Lake. Starting at RS10C, a station that Marc Ohms had surveyed a number of years ago and left hanging, we surveyed down a tight crawl and to our lead in the NW corner of W.C.T.U. Hall. The lead surprised us as it turned into a little maze area with sand and stream cobbles everywhere. We named it the Cobble Maze. We eventually popped out of an obscure hole along the Wild Cave Tour Route and reconnected to station RS10A. From there we backtracked to RS10G to a lead we had bypassed earlier. However, after two shots we called it a night, primarily because I couldn't fit through a tight squeeze just before our last station. We'll have to return another night with skinny people to finish up the last few shots in this area. We ended up surveying 122 feet for the evening.

 

4th Trip: On 3/6/2012, Rod Horrocks led Kenny Slocum & Matthew Chuvarsky to W.C.T.U. Hall in the Historic Section to continue the survey of the Cobble Maze area.

Trip Report: We started our evening trip by continuing the RS10 survey in the Cobble Maze area just off of W.C.T.U. Hall on the Garden of Eden Tour Route. Although we only took two shots, we discovered numerous small bones in the flood debris on the floor. The bones were mixed in with the sand and charcoal and are apparently part of the flood debris. There were also several dead insects mixed in. Boy, would I love to carbon date that charcoal! Such a date would give us a date when that paleo entrance, which must have been located near the Elevator Building, was open to the bottom of Wind Cave Canyon. The charcoal also indicates that the flood happened after a fire had burned the vegetation in the area.

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