Jump to content

Mbs Listed On Topo Maps


Muzikman
Followers 0

Recommended Posts

On most topo maps some benchmarks are listed. They appear as an "X" and then either the name or a BMxxxx (the xxxx being a 4 digit number).

 

My queston is, what is an easy way to find these in the GC or NGS database. I only way I found (unless it was narked with the actual name) was to plot the coords and then search. This is kind of time consuming and figured it would be nice if there was a way to cross reference the BMxxxx label. If there is no way, what does the BMxxxx desigbation mean? I assume the BM means Benchmark, but the 4 digit number almost seems random.

Link to comment

Good call, looking at the map that would be it. So, since that is tge case, there would be no way to use that number in hunt as there would be many bm's at around the same height. Ok, that answers my question, if i wanna find a bm listed on a topo, I just have to plot it.

Edited by Muzikman
Link to comment

With the USGS topos, not every X with an elevation next to it has a permanent mark.

 

For some reason, the USGS decided to use the same symbol for both permanent marks and spot elevation checks with no mark. The difference between the two is the size of the X which is very, very hard to distinguish on a digital map. It may be easier if you have a hard copy map and the legend on a separate sheet that allows you to place the legend next to the X on the map and compare sizes.

 

That being said, you can safely assume that if there is a BM next to the X, there was a disk at that location at some point in time.

 

If you find an X with an elevation next to it but not the letters BM, you will need to find out if it is a large X or a small x to determine if there was ever any kind of recoverable mark at the location. The large Xes without BM next to them had some sort of recoverable mark (type not specified on map) at that location. The small xes were spot checks with no permanent mark, probably some high point in the area.

Edited by California Bear
Link to comment

If you look at the lower left corner of a USGS quadrangle you will see the "credits" for the map. Today we would call this metadata, which is data about the data on the map. It will list the agencies whose control is plotted on the map. At least in my area you can make a pretty good guess as to who set the mark.

 

If you have a line of levels along a railroad or highway where every bench mark is shown with an "X BM ####" with the #### being the nearest foot elevation it is probably NGS or its predecessor the USC&GS. These should be in the database here.

 

If you have a line of levels along a railroad or highway where there are "X BM ####" and "X ####" marks then it is probably USGS or another agency and not likely to be in the Geocaching database. The "X ####" marks are something other than a bench mark disk such as a chiseled square or some other physical mark.

 

If it is an italic X #### it is a spot elevation with no recoverable mark on the ground.

Link to comment

Interestingly I have been reading topo maps for most of my life and just always assumed the "X xxxx" was an elevation and that "X BMxxxx" was a benchmark. I assumed thay if there was no BM, that here were no actual mark (usually peaks of the higher elevated hills). Back when I was young I found a few bm's by just locating them on the map and going and looking for them. This was about 15 years ago and up until geocahing added BM database to the site, I didn't think anyone cared about BM's. Also never realized there were so many. I assumed that they were all on the map.

 

The reason this even come up is because I am researching old coal mines in the town I grew up in. There are remains of what I think was a mine (and growing up my father always said it was a mine) but there is obviously no shaft opening any more. I found reference to four mines in the area. One of which the descrption states that it was .5 miles SE of BM1202. Not even thinking the 4 digit number was an elevation, I was trying to locate BM1202.

 

Herold & Bowers Wagon Mine (ca.1884- ? ), located 1/2 mile SE of BM1202, Monroeville, Patton Twp., Allegheny Co., PA

Owners: (ca.1884- ? ), ?

(ca.1923- ? ), Herold & Bowers Company,

 

 

Country Bank Mine (ca.1923- ? ), located 2 miles N. E. of Turtle Creek Borough, Patton Twp., Allegheny Co., PA

Owners: (ca.1923- ? ), ?

 

I have a feeling that the one above might be the one I am looking for, but wanted to rule out the "Herold & Bowerts Mine" before I dug any deeper into my research.

 

I don't know if any of you saw this post a last month, but the remains of this BM is near what I think was the mine entrance.

Edited by Muzikman
Link to comment

Inspired by this topic, I hit the dirt roads of San Bernadino National Forest with a USGS map. My mission, find marks not in the NGS database using only the USGS map as a guide.

 

I was successgul in finding 4 out of 5. One was a standard disk, two were plaques attached to trees and one was a cairn.

 

The fifth one I may or may not have found. I can't be sure without a description. It was a Third Order or Better with Recoverable Mark but not a tablet. I hiked up to the top of the peak indicated by the X and, according to the GPS, I was at the right altitude but there was no mark, carving, bolt, etc. that I could find. However, the rock on the top came to a very sharp and distinct point which may have been the recoverable point.

 

All in all, I had a great time looking for marks in an environment where the marks aren't being constantly destroyed to make way for homes and strip malls.

 

I haev some pics and will upload them when I get a chance.

Link to comment

The way I do it is to use the Topozone map feature. I get to the location via the maps and put my cursor on the location and then click..........the co-ordinates of that position now appear at the top of the map. (You may have to reset the default co-ordinate datum feature to get a number that means something to you.) I then plug that number into the advanced search feature here at Geocache and get all the nearby BM's. If it exists as an NGS item you will know instantly.

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Followers 0
×
×
  • Create New...