Sub-surface?

[+Fritz_Monroe]

I haven't done any benchmark hunting, but was looking at what was around me. I came across this one. It says that the marker is "set in the top of a concrete post 3 inches below the level of the sidewalk and protected by a cast iron cover."

 

Now obviously this is under the sidewalk, but is there any way that I would be able to actually see this marker? Would the info be on the cover? I'd guess there is some sort of access cover over this thing, but anyone ever find one like this?

 

This has a log entry and I have dropped him an e-mail to see if he found it. Just wondering if this is fairly common in big cities.

 

F_M

[RACooper]

As the description says, there should be a cast-iron cover in the sidewalk (or was at the time that description was made) that, if lifted, should reveal the disk on a concrete mounting. If you're lucky, the cover actually states "SURVEY MARKER", but you may not be able to lift it (could be wedged, or jammed, or the support rim of the cover damaged...) or it could just be plain and unmarked (or even marked as UTILITY or something).

 

I've come across one or two of these on the forums, and one marker I haven't logged (last saw it about 5 years ago, and haven't been back to confirm it yet) where the cover is missing, but the disk is still intact inside an iron rim in the sidewalk. (See BM0028, and look at "BM Disk, Shot 3" on Jumpmaster's log entry for an example.)

[+GEO*Trailblazer 1]

Iron Lid

This is one of the ones I found most recently.

I found another that was a 4" PVC pipe plug with casing.

[+Kewaneh & Shark]

It sounds very similar to GU1074 in Madera County, California, which I found in February. In the middle of the sidewalk, down a few inches, covered by a cast-iron lid, etc.

 

 

There are a few more images on the page for GU1074.

[+Fritz_Monroe]

Well folks, thanks for all the responses. I know what they look like now. I re-read the log of that benchmark and he indicates that he couldn't find it. Knowing the general area, it was probably cemented over many years ago.

 

F_M

[+ventura_kids]

So you will need to bring a jack hammer. The surveyors appreciate any help they can get clearing the access to these markers.

[+GEO*Trailblazer 1]

If the cement is not reinforced with rebar a metal detector might help.

[+California Bear]

I was looking for a benchmark this morning that is listed as being "4 INCHES BELOW THE SURFACE OF THE GROUND". I couldn't find the marker but found an RM for this marker and was able to pace off the distance to where the mark should be. At that location, BM is painted on the sidewalk with an arrow pointing into a flower bed. I poked around in the ice plant but didn't see any obvious markers or concrete (which the mark is allegedly set in).

 

Has anyone ever had to dig to find a marker? And why on earth would anyone place a mark under the ground where it can't be used?

[RACooper]

Sometimes you do have to dig. Many times markers get covered by changes in the surroundings (such as the addition of the flowerbed you mentioned), or runoff from rain depositing sediment, or landowners raising the topsoil (like my dad did in our side yard once, to try and grow grass in soil rather than Central Texas red clay). I had to unbury a marker a few weeks ago with an inch of dirt over it that was originally marked as "level with the ground".

 

Another reason is that some markers seem to be placed slightly below ground level to protect them from mowers and such (usually with a witness post placed nearby). That's strictly an observation; I'm not a professional surveyor.

[+Kewaneh & Shark]

That's a correct observation RACooper. Sometimes benchmarks are placed a few inches underground for protective purposes. In some cases it can be many inches to a few feet down, such as a subterranean marker for a traingulation station. Other times, they just get covered up.

 

In my part of the world, many (many!) benchmarks are placed in agricultural areas, adjacent to, and sometimes in, the ag fields. They are commonly placed on 14 inch by 4 foot concrete post that is set flush with, or just below the ground surface to protect them from the farm equipment. Over time as these fields are plowed and cut and graded and plowed again, these marks get buried deeper, exposed, and sometimes uprooted and destroyed. It's rare to find them as they were originally placed.

Edited December 24, 2003 by Kewaneh & Shark

[+GEO*Trailblazer 1]

Just for the Observation,

I have found that the 40+ year old ones have about 4"-6" iches of TOPSOIL,that would be the accumulation of the years of topsoil growth,most that I have found in remote areas that have not been disturbed.

The AG fields that say 14" underground are approximately 18"-20" now.

I have only foud 1 in the 6 second range off.Usually 2 seconds,most are accurate using descriptions.

(NGS 6 seconds)

 

The 60-70 years range are usually Railroad Survey Bench marks and tend to be a little farther off in coordinates but are easier to find with the description and being along the Railway and in the Bed of the Tracks tend to have the ^" of topsoil range,and the ones set in bedrock always have about 3-4 ".

 

The One's from 80+ years are usually larger stone,or Chisled in Stone,and most of the finds have been by desription.

 

I try to keep track of all the detail I can and then there is always something you forgot to write down.

 

If we were to (really recover) a mark to its greatest details,

Which would really be the proper way to do it!

Would entail so great a detail us BEGINNERS do not even understand yet.

 

Astronomical Observation.

All the measurements to all the other marks and references.

Details of Terrain,

Distances and directions to all other survey points in the Control.

Condition of mark(s)and refs.

and there's lots more detail that should,could and would be useful in Investigations.

 

So I guess found fits?????

[+Black Dog Trackers]

epolk -

 

There have been many discussions here in the past about benchmark hunting kits that people make. One of the things in mine is several-inch piece of stiff wire, about like coathanger wire, that I have folded in my kit. The wire can be used to probe the ground in the suspected area to find the disk and the circular cement around it. That saves you the trouble of digging, which is especially good to avoid in landscaped areas. If my wire won't reach the disk, then I'm probably not going to dig for it, and will instead log it as Not Found.

 

Some people use metal detectors, and although I have one, I prefer the stealth mode too much to use one for benchmark hunting.

 

As I have seen, surveyors have no problem with digging through surface material to get to the disk - that's their job and they're expected to do it. We don't have any business (pun intended) digging up the disks, so we should be more delicate about it if we do dig. There is one that Artman and I had been looking for and not finding, but one day I was driving by and noticed a lot of spray paint in the area. I looked and saw that a flower bed in the Post Office parking lot had been dug up and there was surveyor spray paint all over the place (rather overdone, I thought). I saw the mark exposed in its 5 inch deep hole in the mulch. It was clear that the surveyor had dug a couple of holes (still there) in the area before finding the mark.

 

It isn't true that a survey mark 'cannot be used' if it is buried. A surveyor will dig away what's covering it, set up a tripod over it and do their surveying with no problem.

 

I generally skip the ones that say they're buried, unless there is a distance fix in the description that gives me confidence that I could determine the location within a couple square feet. With my GPSr showing a 13 foot zone of accuracy, the number of square feet I'd have to search below ground is too much.

[+California Bear]

Thanks all for the input! I might jave to add a coat hanger to the items I carry. When I get one, I will go back to that spot and check again.

[+GeckoGeek]

Thanks all for the input! I might jave to add a coat hanger to the items I carry. When I get one, I will go back to that spot and check again.

I got a cheap long narrow screwdriver I use for that. I think the use of a "real" tool rather then some wire makes you look more official - or at least like maybe you belong there.