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Those Topo Map Bm X's


IncitatusMaximus
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OK, I have a question that's opposite to the good old "I've found a brass disc thingy but it's not on geocaching.com."

 

Whip out your favorite topo program, whatever that is, and take a quick journey with me to the wild west. Yankee Jims is a good place to start (N39.039712 W120.883011). On the topo is printed BM 2575 with an X. So far, when I've seen these printed on the topo, they correspond with an entry in the NGS database. This one doesn't. Nor does BM 1749 to the northwest, nor does BM 969 at the gauging station to the west of this one.

 

OK, now I'm intrigued. I've always loved this area. I think wild west mining appeals to the kid in me. I'd love to see the historical datasheets for these marks. Maybe there's an interesting story or something in there.

 

The first question, to rule out the "it's still stuck in a filing cabinet" answer, is are the BM's on topos always present (provided they aren't destroyed) in the NGS database? Or do they use other sources too? And if the answer is "yeah, it's probably still stuck in a filing cabinet," is there any way to research this outside of what's online?

 

Thoughts / opinions / rants / raves?

 

OH, P.S., slightly non-benchmark related, but check out what's at N39.019036 W120.919663. I've been told it's actually still there too, but I haven't figured out what it's for or how you get to it yet.

 

Edit: Corrected coordinates for initial BM.

Edited by IncitatusMaximus
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OH, P.S., slightly non-benchmark related, but check out what's at N39.019036 W120.919663. I've been told it's actually still there too, but I haven't figured out what it's for or how you get to it yet.

I've been wondering the same thing. I've found "BM" and an elevation on several of my topo maps but with no coresponding disk or other monument in evidence. I also can't find any such record in the NGS database. I figured it was just because the places I've been looking just happened to be in the Olympic National Park and that the marks fell under a different jurisdiction.

 

Oh, and as to the item at the specified location, I should think it's purpose is obvious. Crossing the river on foot. As to how you get there, I'd suggest parachute drop. <_<

 

R_C

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The topos are a product of the U.S. Geological Survey (USGS) who used a variety of differenct sources for their survey control data. Look in the bottom left hand corner and you will find a note that specifies "Control By" followed by the designeations of the agencies whose survey data USGS used for that sheet. Most often they will be USGS and USC&GS (now NGS), sometimes USACE, TVA and a few other agencies. If you can't find the mark in the NGS database then it's a mark of one of these other organizations which in most cases is USGS. Unfortunately only a very small percentage of the marks set by USGS were ever submitted to NGS for inclusion in the National Spatial Reference System. You will need to contact USGS for information on the mark.

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IM, since you're in California, you may be interested in the USGS survey mark reports for the Yosemite area that I obtained from the agency. You can find PDF files of them at www.planetzhanna.com. I think every BM X on the Yosemite 7.5' quads is accounted for in those listings. Well, every one I've double-checked so far, anyway. :-)

 

Patty

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