Hunting Benchmarks with a metal detector?

[+snowfreak37]

This benchmark is not really of any importance to me except it's fairly close by and its proving to be more difficult than I thought. The first time out I only had my GPS'r and the datasheet. Even though the location is scaled I was hoping to find this rock outcrop with my eyes only. That didn't work so I walked to the the west end of the north guard rail and walked roughly 149.5 feet to the east(I have around a 3 foot stride) and walk roughly 54.2 feet north from the center of the road. There is a small portion of exposed rock outcrop and I kick away some of the loose dirt and find nada. Today I went out with my handy dandy measuring wheel and went an exact 149.5 (which was within a foot of my rough calculations the first time) and measured an exact 54.2 feet. The other measurement from the telephone pole is obsolete they have been moved since 1973. In fact its quite possible that the guardrail has been lengthened or shortened since 1973. However this is the only rock outcrop for a distance, so I believe I'm in the right area but quite a bit of the rock outcrop is covered with 3-5 inches of soil, grass, brush which leads me to the metal detector question. I can borrow a friends metal detector and it has the ability to detect different metals. What are these benchmarks generally made of? I have never used a metal detector before so I guess I am looking for some input on what to expect. It's got to be better than digging through the dirt.

 

On a seperate note when I measured from the center of the road I used my measuring wheel and the benchmark is down a fairly steep embankment. If I took a piece of string and cut it 54.2 feet it would put me further north than my measuing wheel. Not sure if the measurment is line of sight (cut string) or how I am doing currently doing it. Thanks for any input.

[+Holtie22]

Unless noted otherwise, distances given in the datasheet description are horizontal, as opposed to slope (cut string), or along-the-ground (measuring wheel) distance. This is achieved by holding the cut string (or measuring tape) level while using a plumb bob to transfer the measured distance down to the ground. The slope distance will always be longer than the horizontal distance. In your case, the 54.2 feet would fall even further north of the centerline than what you measured with the cut string. Does this still put you on a rock outcrop? If not - Could it be on McDonald Road? When was the State Highway moved?

[Bill93]

Search the forum history for discussions of metal detectors.

 

The disk is usually bronze, and with its surface area and high conductivity it gives a pretty good signature. Most treasure hunter type of detectors will do your job. Even a cheapie will find them under a very few inches of dirt and the better ones several inches.

[+snowfreak37]

Unless noted otherwise, distances given in the datasheet description are horizontal, as opposed to slope (cut string), or along-the-ground (measuring wheel) distance. This is achieved by holding the cut string (or measuring tape) level while using a plumb bob to transfer the measured distance down to the ground. The slope distance will always be longer than the horizontal distance. In your case, the 54.2 feet would fall even further north of the centerline than what you measured with the cut string. Does this still put you on a rock outcrop? If not - Could it be on McDonald Road? When was the State Highway moved?

 

The 54.2 feet even further north would still be on that rock outcrop. The only measurement I have made so far was with my measuring wheel. I was considering cutting a piece of string but do not intend on going that route. Even though the coordinates are scaled I am quite certain its off of Route 11, there are no guard rails whatsoever on McDonald road. I am not sure when the State Highway was moved. At least I have a general area to concentrate on now. Just need to borrow the metal detector and dig in.

[Bill93]

I don't remember when NGS did the scaling - it was either the 1970's or 1980's I think. I suspect they used current maps at that time to get the highway numbers. I have seen several cases where the descriptions written in the 1930's called for a road number, and the SCALED coordinates were taken from a map where the road number had a newer different route, resulting in the scaled values being off by miles.

[+t8r]

Don't forget the distance from the pole. They don't move those very often, if it is there at all.

When you get the metal detector in hand, take it to an easy benchmark and test it's reaction to the bronze disc.

My metal detector is about high end of the cheapies ($100) and will detect the discs about 5 0r 6 inches underground.

[+pgrig]

After about a year using my Garrett Ace-250 machine (about $200), I find it's useful in perhaps 40% of the problem situations I hit. I usually set it for "All Metals" and use its "pinpoint" feature to see where it lets off the loudest signal. It seems to detect things down to 6" or more.

 

Problem comes from its getting fooled by bits of metal trash that are so prevalent nowadays. As much as 1/8 of a cola can sounds like a benchmark disk. Rather small scraps of tin foil, pull-tabs, etc. set it off, and are hard to discriminate from disks. Also it seems to "miss the mark" quite often by 6"-12". This may not sound like much, but if you're digging down 6" through hard terrain, it's a pain!

 

I usually use it only as a last resort, when taping is very hard or measurements have been made but are inconsistent (or logically impossible). But it has found me a significant number of marks that otherwise would have remained hidden. [Particularly memorable was a disk that was planted for one of the old Nike missle sites that used to ring Boston but which have now been replaced by subdivisions, wiping all tie-ins and RMs away in the process.] Now if they would only make a machine that would detect a "drill hole in ledge," I'd be a happy man....

Edited May 27, 2009 by pgrig

[+skeezicks]

I have found a couple using a metal detector.I got approximately where they should have been by the description and finding the reference marks, but had to actually find them with a metal detector.They are a nice big target for a metal detector and you will know them right away when you find them...they give off a huge signal compared to something small.I ran my metal detector across my wedding ring to get a small sized signal indication,so when I found a signal a lot bigger than that,I knew that had to be it...unless luck is against you and there is an old steel can right beside it ...Here are a few of pictures of the two I was talking about.

 

The first one is the benchmark "Bend" (RW0552)

 

 

This one is for the benchmark "B 451" (RX0021).This one I carefully folded back the grass and placed it back when I was done, so that you couldn't even tell I had been here.It was in a park is why.

[Bill93]

You've got to check the rules in parks. Many (most?) have a prohibition on using a metal detector. There are two reasons, first that some people aren't as careful as you to cover their divots, and second that many parks have archaeological items that they don't want disturbed.

 

I've heard that in National Parks you can get arrested for having a metal detector in your car and not even getting it out.

[+skeezicks]

You've got to check the rules in parks. Many (most?) have a prohibition on using a metal detector. There are two reasons, first that some people aren't as careful as you to cover their divots, and second that many parks have archaeological items that they don't want disturbed.

 

I've heard that in National Parks you can get arrested for having a metal detector in your car and not even getting it out.

 

I agree.This was just a small park where people picnic and bring their dogs,etc.. to. My brother in law found out the hard way about a national historical type park.He was just inside of the border of one and didn't realize it until they came to his house and threatened to arrest him and also confiscated his detector and fined him...they had him on camera.

[+Harry Dolphin]

I borrowed a CoinMaster once, but did not have a lot of luck with it.

I got questioned by an NPS employee once, for 'looking like a turkey in the woods' during turkey season. (I DO NOT look like a turkey!) You can hunt turkeys, but you cannot use a metal detector to find a benchmark... Sounds like the red tape got badly tangled somewhere. Of course, you're not allowed to dig in NPS areas either. There's a series of Setting 59, labelled as 2" below ground level. I cannot find those suckers!!! Oh well. Sounds like I should just stay away from DWGNRA.

[Difficult Run]

I have been able to find triangulation stations within National Park boundaries, but I do it with extreme caution....

 

My hiking pole is actually a homemade probe with a 1/4" stainless steel rod on the end.

It takes practice, but I can tell when I've hit the "mark" or just a large rock. At this point I just expose the disk with my fingers, using no digging tools.

(It's remarkable what a probe can tell you just by the tone it makes hitting an object.)

 

Lots of practice and patience required.

~ Mitch ~

[+snowfreak37]

Thanks for all the replys so far. I borrowed my friends metal detector and the markings say Bounty Hunter Pioneer EX. He's trying to find the owners manual but it seems easy to operate. It has 3 depths settings Shallow,Medium, and Deep of course I am not sure what kind of depth they correspond to. The top section has 4 Probable Target options Iron/AL ZN/AL 5 cents/COINS. It will probe for all or you can reject the ones that you want to. I am not sure if I should leave it in the find all mode or reject a few of them. It also says it needs to stay in motion to detect objects. This one seems to make the same noise regardless of how big the object is. Now all I need is some dry weather and some luck to find this benchmark.

[+PFF]

You seem to be taking the wise approach; i.e., getting some practice on known objects before hunting for a benchmark.

 

The preferred setting probably will be "coins". (Disks are on the opposite end of the scale from Iron.) You can search in the widest mode, and use the selector switch to determine what you're picking up.

 

The instruction book probably is online. Even if you don't find the exact model, the directions will be similar for other units made by the manufacturer. You are correct about the search coil needing to be in motion. (The exception is high-end units which feature a "Pinpoint" mode.)

 

Disks often are slightly recessed within their mounting objects, whether it is a cement monument or a rock outcrop. Consequently, dirt and leaves tend to accumulate in the depression--obscuring the disk from view. I find my detector to be very useful, even when the data sheet says "flush with the surface of the ground".

 

Ditto for what was said about National Parks, and add State Parks.

 

-Paul-

[68-eldo]

Thanks for all the replys so far. I borrowed my friends metal detector and the markings say Bounty Hunter Pioneer EX. He's trying to find the owners manual but it seems easy to operate. It has 3 depths settings Shallow,Medium, and Deep of course I am not sure what kind of depth they correspond to. The top section has 4 Probable Target options Iron/AL ZN/AL 5 cents/COINS. It will probe for all or you can reject the ones that you want to. I am not sure if I should leave it in the find all mode or reject a few of them. It also says it needs to stay in motion to detect objects. This one seems to make the same noise regardless of how big the object is. Now all I need is some dry weather and some luck to find this benchmark.

 

Does the manual look like this?

[+snowfreak37]

Thanks for all the replys so far. I borrowed my friends metal detector and the markings say Bounty Hunter Pioneer EX. He's trying to find the owners manual but it seems easy to operate. It has 3 depths settings Shallow,Medium, and Deep of course I am not sure what kind of depth they correspond to. The top section has 4 Probable Target options Iron/AL ZN/AL 5 cents/COINS. It will probe for all or you can reject the ones that you want to. I am not sure if I should leave it in the find all mode or reject a few of them. It also says it needs to stay in motion to detect objects. This one seems to make the same noise regardless of how big the object is. Now all I need is some dry weather and some luck to find this benchmark.

 

Does the manual look like this?

 

It does now

[+snowfreak37]

I tried using the metal detector this weekend to find the benchmark. I searched in my backyard first to get a good idea on how to use it. It got to the point where I could (see) the object above ground. I found nails, staples,cans,bottle tops, a large 1"x4' piece of metal that's still in the ground ( I was catching hell from the Mrs from the holes in the ground) but honey its only the back yard. My most exciting find was the key that I lost late this winter and still works like a charm. I didn't find the benchmark. I searched a very large area and came up empty handed. I measured from the existing poles(which have been replaced) 179.2 west which put me well beyond the rock outcrop but still used the metal detector and found nothing. Ironically from my initial search point I measured 179.2 east and one of those 3ft high green cable upright posts was installed. There was also a 4ft section of old telephone pole lying in the vicinity. I really think I'm in the right area just can't find this mark. I returned the metal detector and have given up on this mark. At least I found my lost key so not all was in vain. Even though I came out empty handed I could see where one of these devices would come in very handy for situations like this.

[Difficult Run]

I returned the metal detector and have given up on this mark.

Hate to see you give up on this mark completely... try it again at a later date, maybe late fall or early spring.

Those 3.5 inch brass disks will make a detector scream, much like a flattened soda can.

A good detector can read them buried a foot below ground level.

~ Mitch ~

[+snowfreak37]

I returned the metal detector and have given up on this mark.

Hate to see you give up on this mark completely... try it again at a later date, maybe late fall or early spring.

Those 3.5 inch brass disks will make a detector scream, much like a flattened soda can.

A good detector can read them buried a foot below ground level.

~ Mitch ~

 

When I went back this last time I really over estimated the amount of soil on the ground. I think the deepest part was around 3 inches of sand. Much of it was lucky to have an inch of soil. I may very well come back this late fall. There was a bunch of blueberry bushes in the area which made it hard to get close to the ground and keep the metal detector in motion. I really expected to come up with a find. Who knows maybe I'll bump into someone that has an upscale metal detector and try that too.

[Bill93]

Have you taken a look at McDonald Rd, just in case the highway was moved? (See Holtie's and my earlier posts)

[+snowfreak37]

Have you taken a look at McDonald Rd, just in case the highway was moved? (See Holtie's and my earlier posts)

 

I have not checked on McDonald Road. There are no guardrails on McDonald Road currently and there isn't a spot where the road is 7' higher than the surrounding land. It can't hurt to check though. The area I have been checking matches the landmarks listed on the datasheet. There's guardrails, the road is at least 7' higher, and there is a pretty good sized rock outcrop. I realize the coordinates are scaled but the GPS'r reads around 50ft at GZ if I follow the datasheet directions instead of the listed coordinates. I'll take a spin down McDonald Road and at least check the area. I have someone I can ask to see if McDonald Road used to be Route 11.

[+Holtie22]

Sounds like you're getting pretty close. The guardrails and telephone poles could have changed considerably in 36 years, but between the 0.8 mile from Cannon Corners and the elevation of 622', I'm guessing it's no more than 140' NE of GZ. Does the rock outcrop extend that far?

 

[+snowfreak37]

Sounds like you're getting pretty close. The guardrails and telephone poles could have changed considerably in 36 years, but between the 0.8 mile from Cannon Corners and the elevation of 622', I'm guessing it's no more than 140' NE of GZ. Does the rock outcrop extend that far?

 

 

The rock outcrop is fairly narrow say around 50ft east to west, but it extends to the north around 100ft which would put it well beyond the 54.2 feet from the middle of the road. I combed over that enitre area at least 3 different times with no results. I was hoping there would be some indication where that old telephone pole was. A hole in the ground, a left over pile of stones, part of the pole still in the ground but I couldn't find anything that was of any help.