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Finding A Benchmark On The Site.


thumper242
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I was wandering through the forest, and found a benchmark disk. Right next to a bearing tree, so easy to find. It was unplanned though, so I wasn't out looking for it.

 

Anyways, I took a GPS reading standing right next to it, but forgot to take down any more info.

 

When I search for a benchmark by GPS coords, it gives me nothing. What am I missing

here?

 

By the way, the coords are N 45.27.279 W 123.22.917. javascript:emoticon('<_<')

smilie

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Thumper,

 

The Geocaching game Of Benchmark Hunting is primarily based on monuments that were placed in the field by the National Geodetic Survey. Early on, This same agency was known as the Coast and Geodetic Survey... Anyhow, they are the developer of the Database that Geocaching uses.

 

The USGS, US Geological Survey is a different agency all together, yet they too have a lot of survey out there you may find. Some of it was submitted for inclusion to the NGS but most was not. They were the primary user of bearing trees for their data and survey purposes. You will not find too many bearing trees in the geocaching database because they were not in the NGS database. And a good many other monuments in the field will not be in there either. Most of these agencies do not share all their data with one another, as the data is for use in different missions and uses different criteria for the settings.

 

The best way to hunt a Benchmark is to first, look for what is in the field where you will be hunting by looking at the geocaching.com benchmark page. Just add your zip code or latitude and longitude and it will tell you what is available for you to hunt and file a find for. if it is not in there it is not part of the game.

 

For a more detailed explination, Have a look

Here.

 

Good Luck Hunting!

 

Rob

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Right next to a bearing tree, so easy to find.

Since it was near a bearing tree, I suspect it is actually a Section corner monument, not a bench mark or control point.

 

evenfall,

 

Bearing Trees are used most by the BLM (f.k.a. the GLO) as references to section corner monuments set by them.

 

NGS sets reference monuments for their control points, not bearing trees, as bearing trees are not very accurate to use for replacing control points.

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Boundsgoer,

 

You are correct, The BLM has set a lot of bearing trees. Here in the Puget Sound area, I have found quite a few set by USGS as well. In Western Washington, there is not near as much BLM Survey here as there is in Eastern Washington and other States. This is a Coastal and Mountainous area and the USGS set a lot of survey in this area for their mapping programs and topo work down through the years. A lot of it was Bearing Tree. Lots of trees around here! Due to the Coast and Puget Sound with all it's many Islands, there is literally a ton of NGS work in the ground here locally too. Usually there is more leveling than triangulation almost anywhere you go, but in these parts both are on par or maybe even more triangulation in some areas. When you include landmarks to the list in third order horizontal control alone, you could just about swim in triangulation. Especially about 75 years ago.

 

I think I did say in my previous post that I didn't think we would find many Bearing Trees in the NGS database as it is primarily involved with a different mission. Geodesy. Trees are not a stable monument for geodesy, They just wont work well for triangulation and leveling work, though they have been suitable for PLSS work forever! :-) I have driven a few railroad spikes in trees over the years for use as a TBM as well, but that was usually the end of the level line I ran for the purpose and it was primarily used as a TBM for Construction Laser calibration...

 

As Surveyors we both know that we could go on and on about how many types of survey monument could be found in the field, but for the purpose of geocaching there is only one kind that matters. Primarily that of the NGS database and that which has been submitted to it, that passed the stability to be included in it. You would be surprised how many people find monuments of every kind in the field and do not understand why they cannot use it for geocaching, and why it will never qualify for geocaching. That was just a quick explanation, most of the answer is more than most people want to know.

 

Rob

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mrh,

 

Nice Find!

 

TBM is an abbreviation for Temporary Bench Mark. They look like what you found and can be found with variations on that theme, or can often be a railroad spike driven in a tree trunk with a piece of lath nailed above it. The elevation at the top of the spike is written on the lath so that constructors can use it as a point for their own leveling, and calibrating their own instruments to known elevations during construction work. The one you found is a lot more official looking than any I usually set. For the most part the tree will not be a stable place to place elevation control for long so it will only be accurate for long enough to do a job without needing to be re-checked.

 

There are however other ways to set TBM's. Hubs and Hubs with a Tack, Hubs with a Blue Feather called Blue Tops which though not a Bench Marked Elevation per se, it is a form of certified grade, which is certifying that a road sub grade has been surveyed to a finished design sub grade elevation. The feather is nailed to the top of the wooden hubs so that you do not lose the location of the hub as you spread material over it to attain the design grade with a bulldozer or road grader. A hub may also have a lath set next to it explaining what it is, as well as any other info pertaining to it which help constructors arrive at a designed elevation or contour. A Nail driven in a street or side walk can also serve as a TBM and even a painted circle with a dot in the center can sometimes signify a TBM. That is a very temporary BM.

 

Mainly they are set as a temporary known point of elevation part of a Survey or some other task at hand.

 

One of the funny things we say in the industry is that if you are waiting for a dump truck to bring you something or take material away, just drive a hub in the ground and a truck will be by in five minutes or so to run that hub over. :-)

 

Boundsgoer,

 

I am sorry, but I don't have a picture. You are correct though, BLM GLO was the primary agency to set Bearing Trees as part of PLSS work dating well back to at least the early 1800's. I will have to keep my eyes open for the Markers I saw. It has been a while.

 

Rob

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fwiw

 

The Nat'l Forest Service USDA is still in the practice of setting Bearing Trees on their lands. The Ottawa NAT'L Forest is in my area and every corner they have found or set will have 4 bearing trees. They often paint a red ring around the tree, blaze it and attach a sign to the effect, Bearing Tree, bearing and distance to corner.

 

The tree on the left is a Bearing Tree of the USFS

 

USFS-1.JPG

USFS-2.JPG

Edited by elcamino
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