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Disappointing NGS description


ArtMan
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I spent a half-day in the hot sun yesterday chasing down some marks across the river from St. Louis.

 

One that had me stymied was JC1145 (NGS) (Geocaching). This is a stainless steel rod placed on top of a levee, alongside the road that runs on top. The published coordinates are scaled, and seem to be about 100 feet from the levee road. Aside from the distance from the center of the levee road and an elevation of 0.1 meter below the top of the levee, the only tie is to a witness post that — you will probably have guessed by now — has somehow vanished since the mark was monumented 30 years ago.

 

JC1145'DESCRIBED BY NATIONAL GEODETIC SURVEY 1981

JC1145'1.0 KM (0.6 MI) SW FROM CAHOKIA.

JC1145'1.0 KILOMETERS (0.6 MILES) NORTHWEST ALONG TOP OF THE NORTH LEVEE OF

JC1145'THE OLD PRAIRIE DUPONT CREEK FROM THE JUNCTION OF STATE HIGHWAY 3 IN

JC1145'CAHOKIA, TO THE MARK ON THE RIGHT, 2.59 METERS (8.5 FEET) NORTHEAST OF

JC1145'THE CENTER OF THE LEVEE ROAD, 0.46 METERS (1.5 FEET) NORTHWEST OF A

JC1145'METAL WITNESS POST.

JC1145'THE MARK IS 0.46 METERS SE FROM A WITNESS POST.

JC1145'THE MARK IS 0.1 M BELOW TOP OF LEVEE.

I paced the area where I felt this station must be about four times without seeing anything. Possibly it is overgrown or under gravel from a realigned levee road, but with all due respect to the NGS (really!), I sure wish the party that set this mark back in 1981 had measured off the distance from the road, since I think there's a pretty good chance this is still on top of the levee. Somewhere.

 

~ArtMan~

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At 8 1/2 feet northeast of the center of the levee road it could very well be in the road now. If the road has been widened to the standard road width (12 feet per lane) you will need a metal detector for this one. If the road has not been widened then it should be right at the edge of the road.

 

John

 

PS: Did you by chance park your vehicle right on top of it? :P

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Artman, after messing around with Google Earth for about an hour, here's my thoughts (Not that I'm right, but here goes anyway). Measuring the distance from highway 3 NW .6 miles puts the mark approx 300 ft WNW of the scaled coords. It appears the road has shifted approx 15-20 ft but to the SW which would put the mark that much further NE of the levee road. I see the road isn't directly on top the levee so they may have added ballast to the top of the levee but hopefully SW of the road. My best guess for a location would be at N 38°33.236, W 90° 12.158 approx 20-28 ft NE of the existing levee road. I'd use the old metal detector if you have one. Since the post is probably broken off, there should be two signals to detect instead of one. Best of luck.

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The NGSers had two things which makes it hard to follow in their footsteps:

  1. topographic maps - the field party had a map with all the marks plotted, which reveals many details not found in the text. NGS stll has these topos, but no convenient way to distribute them.
  2. practice - if you walk the entire bench mark line, you get to know the marksetter. After a while, you don't even need the description, you just see through the marksetter's eyes and walk over to where you'd set it.

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Thanks, all, for your thoughts. Comments in order ...

 

John, The 'road' is currently a gravel bike trail (though adequate for one-way vehicular passage. I didn't measure it, but it's probably about 12 feet wide. I concentrated my search a few feet to the northeast of the northeast edge. Unfortunately, I don't have a metal detector, which might have been exceptionally handy in this case.

 

chiknlips45, I based my search area on the scaled coordinates. After reading your post, and using Google Maps, I approximated the distance from the intersection of the levee road with highway 3, and like you I came out a couple of hundred feet northwest of where I had focused my search. However, I did go out on the levee (northwest of Water St) to approximately the point measured and didn't see anything. But the distance (1 km / 0.6 miles) is, I suspect, based on a vehicle odometer, which means it could be plus or minus 1/20 of a mile — another 260 feet or so — and when I go back, I'll explore a greater distance northwest from the road.

 

I'm not sure where you got the idea that the road is not on top of the levee; it is, except where it dips down to grade level at Water Street. I'm a transplanted Easterner, and levees are new to me, but it looks like the road originally followed the levee, crossing Water Street at levee-top elevation, rather than dipping down to the road on a more northeasterly alignment. There would have to be a bridge over the road then, and possibly it was removed to allow taller trucks to pass. I don't know. The 1989 Cahokia quad seems to show the levee road going right through, though this may be a simplification.

 

AZcachemeister, as a former federal employee, I have to note that (1) NGS records may include maps and field notes that are not published on datasheets and which may aid in recovery, and (2) it's not the oft-abused federal employee who may have to take six hours to find this station. That honor goes to some oft-abused state or county employee, or surveyor or engineer who will pass the cost on to the client.

 

joegeodesist, good observations, both, but alas not very useful to us. Some non-federal jursidictions have published datasheets that include diagrams of station locations (Arlington County, Virginia, and St. Louis County, Missouri, are two that come to mind). A picture really is worth a thousand words.

 

John (again), I think you're looking at the wrong levee. There are two levees at this location, and the datasheet specifies the north (actually northeast) levee. The benchmarks that are marked on the topo map (415 and 423) are on the south levee. Also, except for the intersection with Water Street, the levee does run on the top of the levee.

 

~ArtMan~

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Don't forget the elevation of the mark, itself. At 430 ft. it is 7 ft. higher than the level of Water Street where it crosses the creek, and only 4 inches lower than the top of the levee. (Those x's on the topo are most likely spot elevations, not BM's.) I think I would focus further NW of Water Street - closer to the 1000 meters from Route 3. (You're right, though about the margin of error) A metal detector would surely help. Do any of the other marks in this series (steel rods) have any sort of housing?

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