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That photo looks really strange. Is it me or does that disk look larger than normal?


EDIT: That photo isn't photoshopped is it? The more I look at it the stranger it looks. Disk is in focus, but the feet are not. The shadow is cast on the sand, but not the disk. Just looks odd.

Edited by Muzikman
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This disk is in the dunes just west of Yuma, AZ.


I think the pic was taken on a macro setting with the focus being on the disk. He may have stopped down the camera some to get better focus.


elcamino-after re-reading the post where I found this it is a boundry marker.

How/where did you find your info? Do you have a map or coords to it?



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That photo looks really strange. Is it me or does that disk look larger than normal?


EDIT:The more I look at it the stranger it looks. Disk is in focus, but the feet are not. The shadow is cast on the sand, but not the disk. Just looks odd.


I thought that at first too but it looks like this benchmark is on the top of a stake or pipe or something that puts it up in the air. THat's what I get from looking at the shadow and the fact that the disk looks so big and is in focus while the sneakers are a little blurry.


I think it looks really cool and odd at the same time.


EDIT: I posted this before seeing the second picture...looks like my guess was right

Edited by geojmetz
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Mike330R, as Mike (elcamino) mentioned, the disk may not be in the NGS database that Geocaching.com uses. However, you can run a benchmark search around its coordinates and see whether it shows up in the results. That's the only way I know of to find a specific mark in the GC.com database when you don't have its PID, since there's no way of searching on the designation.


However, you *can* search by designation (station name) at NGS's site. But I just tried "AP 7" and "Arizona" and didn't find anything. :-( Still, it's a good technique to keep in mind for the future.



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That's the only way I know of to find a specific mark in the GC.com database when you don't have its PID, since there's no way of searching on the designation.

You can actually search by designation on GC.com, if you use the Advanced Benchmark Search page. It's a little fussy, but I can usually get decent results and there have been quite a few times when it's come in handy.


I'd still go directly to NGS for the most current datasheet, however. The GC.com versions are outdated.



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Hey All,


This is a Cadastral Survey marker, and it belongs to the Bureau of Land Management, General Land Office. It is a marker used with PLSS survey work, and used as the frame of reference for legal property descriptions. This is an angle point like Callaway mentioned, and many of these Cadastral Markers are set on top of a stand pipe like this one is. This Angle Point is number 7 within this particular Township and Range. This type of setting is generally not stable enough for geodetic work. The NGS has often set their markers at the POB of the meridians and baselines, but since these Cadastral Markers measure Township and Range location which is basically a series of six mile by six mile boxes, they don't really apply to kinds of control used for geodesy.


This particular marker belongs to San Bernadino Meridian. It is located 120 miles east, and 102 miles south of the San Bernadino Meridian Baseline, which is considered the POB, or Point of Beginning for that particular meridian system, one of three in California.


In a nutshell this marker helps to define the Township and Range system. It is a sort of coordinate grid system, but not to be confused with UTM. It is not a Datum, yet it has used Datum down through the years to help map and define itself. If you are interested in learning more about this system used for defining real property, here are a few good links. The online information regarding these is quite exhaustive.


http://www.blm.gov/cadastral/meridians/meridians.htm is a link showing all the meridians in all the states that use this system.


http://www.blm.gov/cadastral/ is everything you will ever want to know about Cadastral Survey work. The Manual of Surveying instructions 1973 found in this link is very detailed and is also available as a .pdf download for those who may want it. It is a large file, or if you like, there is also an html version also.


http://phoenix.gov/ASSOC/plsshelp.html is a brief overview of the Township and Range System.


Enjoy, Rob

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Hey All,


Taking Callaway's example a little further, here is a link to the other side of T17S R20E This location is six miles east of Callaway's photo.


While we look at that photo on topozone take note of the angle of the Mexican Border, which is also the border line known as T17S. These Maps are oriented North Up so the border line for California is on a bearing of roughly 260 degrees. Meridians are laid out as a line running North/South. Baselines East/West. So all the boxes of this coordinate system are for the most part laid out square to this orientation. With 270 degrees being true west, this border is on an angle. I know this seems obvious, but when you look at the Cadastral Marker again, notice the angle of the line drawn on the marker. It matches the angle of the border line. and this marker is a point on that angle, that is why they refer to it as an Angle Point. Once this line travels six miles further south it will likely become known as T18S and will increment higher each six miles south, and once it crosses the San Bernadino Meridian The Range markers will change from RxxE to RxxW. As angle points go in other cases, A surveyor will use the term angle point to describe a point, or place on a curve or tangent where an angle that changes the current direction, bearing or heading is located.


One of the interesting features of cadastral markers when you find them is there will be lines on them that depict the lines that make up the township and range system where it is located. At a glance you can see on the monument which area is marked in the territory. If the station is properly oriented, they can help orient you as to the direction things are if you know how to read them. Just remember the usual north up orientation.



Edited by evenfall
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Mike330R -


After you finish learning about the cadastral marker in the picture, you might want to join in the fun of finding the benchmarks on the database we use and log them. A good place to start is the search and benchmark hunting FAQ page. Put a zip code in the "By Postal Code" box and get a list of benchmarks to look for.


Another thing to do is to use the USGS Feature Query. In there, click on the dropdown arrow in the "Feature Type" box and you'll see some interesting things to visit while benchmark hunting; in particular - "summit" (Arizona has 84 summits listed above 9,000 ft.), or "populated place" (Arizona has 15 populated places over 8,000 ft. elevation). Get the coordinates from the USGS page's output and punch it in the coordinates box you find after clicking on "Other Search Options" in the benchmark hunting search and FAQ page.

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Most of all those I have found in the Desert are that way............sand dunes also build up so they placed them high enough not to be covered with the shifting sands.


I have a 2 questions.

What is a A "True Meridian"?

What is a "Standard Parallel"?


The Prime Meridian is 0 00.000* is 0 00.000* from the equator to the pole(N-S)

It would therefore stand to reason that the Principal Meridians are the same,is this correct?


A Standard Parallel say 39 00.000* is 39 00.000* from the East Coast to the West Coast,when placed on a map or chart it appears to be curved due to the curvature of the Earth,but it is still 39 00.000* at all points along that line.

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I am BLM Cadastral Surveyor, and even surveyed near this monument in the early 1980's.


FYI The PR on the bottom of the markings are for the "Public Reserve", that is 60 feet wide along the mexican border. Most of the public land surveys 'close' into the reserved strip and not the border itself.


As someone mentioned, it was probably set flush with the surface but the sands shift. Someone had the forsight to drive a fencepost or something.


The records that describe this type of monument are found in BLM state offices, Cadastral Survey function in that office. In this case, for California that would be in Sacramento.


- jerry wahl

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