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7 Souvenirs of August

Benchmark Hunting

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Using your GPS unit and/or written directions provided by NGS, which are available for review by the public, you can seek out NGS survey markers and other items that have been marked in the USA.

At the top of peaks or in a village square, you probably walk by at least one every day.

In the last 7 days, 666 benchmarks have been logged by 250 users.
Overall, 151589 benchmarks have been recovered in 212289 logs.
There are 736425 total benchmarks in the database.
Last Generated: 8/28/2014 6:39 PM PST

Thanks to ArtMan, Black Dog Trackers, caseyb, Kewaneh & Shark, mloser, PFF, and seventhings for updating the FAQ! (Thanks also to survey tech and Z15 who were among those that participated in the earlier update.)

Introduction

BenchmarkThis FAQ has a lot of information about benchmark hunting, finding, and logging in it. Please don't let that put you off; benchmark hunting is fun! We wanted to write this FAQ to not only get beginners started, but also to serve as a reference for more advanced benchmark finders. A good first step is to read the index below to see what's in the whole FAQ page.

What is a benchmark?

A benchmark is a point whose position is known to a high degree of accuracy and is normally marked in some way. The marker is often a metal disk made for this purpose, but it can also be a church spire, a radio tower, a mark chiseled into stone, or a metal rod driven into the ground. Over two centuries or so, many other objects of greater or lesser permanence have been used. Benchmarks can be found at various locations all over the United States. They are used by land surveyors, builders and engineers, map makers, and other professionals who need an accurate answer to the question, "Where?" Many of these markers are part of the geodetic control network (technically known as the National Spatial Reference System, or NSRS) created and maintained by NOAA's National Geodetic Survey (NGS).

Why search for benchmarks?
The interesting thing about benchmarks is that a majority of them are located in plain sight (though largely ignored by the general public). Searching out these locations and documenting them allows others to share pictures of the various areas where they are placed. There's a certain excitement to be the first to find and document a control point, as well as seeing what others have found through photos on the website's benchmark gallery. Some of these points haven't been visited and documented in a very long time, so you may also be rediscovering long neglected objects of American history as well! :w
Do I need to have a GPS receiver to find benchmarks?
No. A GPSr makes getting to the right area easier, but when you're there, you will (generally) be better off if you use the details of the benchmark's location description to locate it. Because most of these benchmarks were installed prior to the existence of GPS, the benchmark database is geared toward finding benchmarks from the descriptions, not the coordinates. Occasionally, however, a good GPSr will prove to be an invaluable tool in finding a benchmark, especially in situations where the location's description is inaccurate due to development and the passage of time. A good GPSr will also help you get to benchmarks in locations you are unfamiliar with.
Where does the benchmark database come from?
In 2000, Geocaching.com imported a snapshot of the ever-changing benchmark database from National Geodetic Survey (NGS), a federal agency within the Department of Commerce. The NGS database contains all sorts of information about these benchmarks. In the NGS database, each geodetic control marker has a Permanent IDentifier, known as a PID and an associated datasheet of information about it.

Kinds of Benchmarks

Benchmarks can be divided into two general groups. The first group, "vertical control points" are objects that mark a very precise elevation above the standard datum plane (usually referred to as elevation "above sea level"). The second group are the "horizontal control points" - objects with precisely established latitude and longitude. At this point, we should explain that "benchmark" is a generic term that is used here at Geocaching.com to refer to all geodetic control points. In the surveying profession, however, the term bench mark (usually two words) is used specifically for points of known elevation, or vertical control. When the benchmark is established at known latitude and longitude, it is described as horizontal control. The generic terms favored by professionals to describe horizontal control are station or mark, rather than "benchmark".

Vertical Control Marks
These are the true "bench marks". Generally the words BENCH MARK will be printed on them near their rim if the mark is the disk type. Many vertical control marks are not the disk type, however, and can include bolts, rivets, chiseled squares, chiseled crosses, etc.
Horizontal Control Marks
There are several types of horizontal control marks. They differ by which kind of horizontal control system was used in establishing them and the amount of precision they represent. Most horizontal control marks are marked with a disk, but some are other types such as a chiseled cross, bolt, drill hole, etc.
Intersection Stations (a Type of Horizontal Control)
An intersection station is a prominent landmark, such as a water tower, radio tower, church spire, mountain top, or any other type of object that can be observed from a distance. These kinds of "large object" station markers, known as intersection stations because of the way their coordinates are calculated are usually landmarks higher in the air than any surrounding objects, which allows them to be seen from many miles away in several directions. By observing one or more such points through a telescope, surveyors can determine positions on the surface of the Earth through the use of trigonometry.
Triangulation Stations (a Type of Horizontal Control)
A triangulation station is usually a metal disk with a small triangle in its center Generally the words TRIANGULATION STATION will be printed on them near their rim. Its position has been determined by measuring distances and angles from other stations. Triangulation stations, also called tri-stations, are typically associated with nearby reference mark disks and an azimuth mark disk. More about that below.
Other Types of Horizontal Control
There are several other types horizontal control marks. These include traverse stations, trilateration stations, and GPS stations and often those words are printed around their rim. Generally these horizontal control marks are not associated with reference marks or azimuth marks.
Reference Marks
Triangulation stations usually have two or more reference marks associated with them. Reference marks are for helping to keep the location of triangulation stations from being lost and are not actually geodetic control marks. The triangulation station's description has accurate azimuth and horizontal (not slope) distance to each of its reference marks so that it can be re-set from them if necessary. These marks also have arrows in their centers that are supposed to point toward the triangulation station. A few reference marks are surveyed with adjusted coordinates and have their own PID in the database.
Azimuth Marks
An azimuth mark, together with its associated triangulation station, provides an accurate azimuth (like a compass direction) that is based on true North rather than magnetic North. This azimuth is used to orient local traverse surveys. These marks also have arrows in their centers that are supposed to point toward the triangulation station.
Cadastral Marks
Some disks that look like benchmarks exist principally to mark land boundaries. These marks, called cadastral marks, are actually not vertical or horizontal control (geodetic) marks. However, some of these marks are in the database because surveyors have made use of them for geodetic control purposes without having to monument a new benchmark in the area.
List of All Types of Benchmarks on the NGS Site
The NGS list of all types of benchmarks can be found in their Marker Code list. Drawings of various kinds of benchmark disks are on pages numbered 6 and 7 of this NGS document on horizontal control.

Obtaining and Reading Datasheets

Obtaining Datasheets
In order to find a benchmark, you must first get its datasheet, which contain its coordinates and a description of where to find it. There are several ways to get datasheets for benchmarks.
On the Geocaching Site
  • At the top of this page, enter a ZIP code.
  • At the top of this page, click on "Other search options", click the "By Coordinates" button, enter coordinates.
  • At the top of this page, click on "Other search options", click the "By Designation" button, enter the designation stamped on the disk, or part of it.
  • On a benchmark's page, click on "Nearest Benchmarks."
  • On a geocache's page, click on "Nearest Benchmarks."
  • On a waymark's page, click on "Nearest Benchmarks."
On the NGS Datasheets Site
  • Click on "PIDs" to enter individual PIDs or a text file containing a list of PIDs.
  • Click on "Radial Search", then enter the coordinates of the center of the search, and a radius size.
  • Click on "USGS Quad" to enter a topographic quadrangle name.
  • Click on "COUNTY" to select PIDs from all the PIDs in a county. To download a whole county, it's better to get an archived file of all the datasheets in a county from the NGS Yearly Archives page.
Is there a pocket query for benchmarks?
No. What benchmark hunters do as a workaround is download a whole county's worth of datasheets as described in the NGS datasheets section above and then use the BMGPX program available here to convert an NGS .dat file into a .gpx file. Several different programs will read a .gpx file and they will allow you to put benchmark coordinates in your GPS receiver, indicate benchmark locations on computer maps, and store datasheet information on pocket computers.

Reading Datasheets

What are the different parts of a datasheet and what do they mean?
A benchmark may be identified in two ways. NGS assigns each one a Permanent Identifier (PID) in the format AB1234 (two letters and four numerals). In addition, each benchmark has a name, called a designation, with no set format. It could be JONES or E 37 RESET or WASHINGTON MONUMENT 1913.
The main parts of a datasheet are:
  • the PID,
  • the Designation,
  • the Coordinates (and whether they are scaled or adjusted),
  • the Box Score (if the PID has one)
  • the original station description and the subsequent recovery reports. These contain the "to-reach" directions, the mark description, and the distances and compass directions from local landmarks to the station.
NGS Datasheets
The different parts of various sample NGS datasheets are explained (and an index of these samples can be found) on their Sample Datasheets page. The specifications of the fields on the datasheets are given and explained on their dsdata page.
Geocaching.com Datasheets
Geocaching.com datasheets were made by reformatting NGS datasheets. One thing to note is that Geocaching.com datasheets don't have the Box Score part that some NGS datasheets have. However, every Geocaching.com datasheet has a link called "view original datasheet" that is the original NGS datasheet. Note that this original datasheet is from 2000 so if you want the most up-to-date version you will need to get it from the NGS site.
What is the difference between "Location Adjusted" and "Location Scaled?"
Simply put, "location adjusted" means that the published coordinates are very accurate, and "location scaled" means that the published coordinates are not very accurate. The published positions for benchmarks with adjusted horizontal coordinates were computed using advanced surveying techniques and are far more accurate than even the finest handheld GPSr can get. The position of a benchmark with "scaled" coordinates was derived by a human in an office by estimating the location of the mark on a topographic map with a scale (ruler). As such, they can be off by 600 feet or more from the actual position though deviations in the 100 - 150 foot range are more common. Your handheld GPS may be very helpful in finding benchmarks with adjusted horizontal coordinates, but can be nearly useless for finding benchmarks with scaled horizontal coordinates. The good news is that only vertical control points have scaled horizontal coordinates. Trying to use your GPS "GOTO" function to find a benchmark with scaled horizontal coordinates will usually lead to frustration and failure.
How can I determine whether a particular mark is "Location Adjusted" or "Location Scaled?"
  • On a Geocaching benchmark datasheet, the second line under the coordinates will say either "location is ADJUSTED" or "location is SCALED".
  • On the 9th line of an NGS benchmark datasheet, to the right of the latitude and longitude coordinates, will be either the word ADJUSTED or the word SCALED. (Don't confuse this with the next line down, which tells whether the vertical elevation is adjusted or scaled.)
What is a Box Score?
On some NGS datasheets (usually the ones for triangulation stations), there is an area of data enclosed in a box made of dash characters and vertical bar characters. Inside this box are distances and azimuths from the PID to other stations, reference marks, or azimuth marks. Be aware that Geocaching.com datasheets do not include the box score information. However they do include a link to the original (circa 2000) datasheet that does include the box score (if a box score exists for that PID). When it exists, the box score information is extremely useful for finding the main station from its reference marks and vice versa. If you will be looking for a triangulation station, be sure to bring its box score information with you!

Finding Benchmarks

For the Beginner
The first step in any benchmark hunt is to choose some benchmarks to search for and get their datasheets. Do not set out with coordinates only; you must have the verbal to-reach description in the datasheet with you when you go. A good first step is to search around your own Zip Code using the search window at the top right corner of this FAQ page. For your very first trip, select some benchmarks that have recently been found so that you will be sure to see one in person on your first trip. The easiest to find are the ones that have been found by someone else using Geocaching.com and have uploaded pictures showing the mark's location. If none near you have been found by people using Geocaching.com, then choose some that have recovery reports from the last 10 years, since the probability is greater that they are still there, and findable. You should select some that are location-scaled and some that are location-adjusted so that you see what that difference means in the field.
The Hunting Process
When you arrive at the area of a benchmark's location but before you get out of your car, read the datasheet carefully. The first thing to note is whether the mark is location-adjusted or location-scaled. Next, read all the benchmark's recovery notes from the most recent to the oldest. In each recovery note, the most important item of information is the distance and direction of the landmark that is the the shortest distance from the station. Start with the closest landmark of all the recovery notes and see if you can find it. The most accurate instrument you have is your tape measure, not your GPSr, so use the tape measure first. If the mark can't easily be found, continue with the next closest landmark and measure from it to an intersection area with the distance you measured from the first landmark. If you don't see the mark yet, probe the ground in the area with a probe, (benchmarks often get buried) searching for the disk plus its monumentation. If you haven't yet found the mark, read older recovery notes again to try to get more information, since many recovery reports don't bother repeating older recovery information that's still good.
What equipment do benchmark hunters use for finding benchmarks?
Here are some items that benchmark hunters typically carry. What you need on any particular hunting trip depends on the kinds of marks you plan to hunt for and the type of terrain where you will be hunting.
  • Notebook (computer, or paper with pen or pencil)
  • Datasheets (paper or computer)
  • Tape measure
  • Compass
  • Probe (useful for finding benchmarks that might be buried with an inch or two of soil)
  • Camera
  • GPS Receiver
  • Garden gloves
  • Trowel
  • Paper towel, packaged wiping cloths, rags, napkins, or other such material to clean off disks
  • Flat blade screwdriver (for digging and for opening rod covers)
  • First aid kit
  • Mobile phone
  • Metal detector
Can I hunt benchmarks by loading the coordinates for a bunch of benchmarks in my GPS receiver and not bring the datasheets?
Definitely not. You must bring along the datasheet for each PID, either on paper or in a portable computer. The coordinates will get you within 15 feet or so only in the case of location adjusted marks. For location scaled marks, the coordinates could be up to a few hundred feet off. In both location scaled and location adjusted cases, distance measurements given in the datasheet description will provide more precision than a GPS receiver in finding the mark. Your tape measure is the most precise equipment you can bring for hunting benchmarks.
Always ask for permission if the mark you wish to hunt is on private property.
As with any outdoor activity, courtesy to the landowner is top priority. Try to determine from the location description whether or not the mark is on private property. If it is, ask for permission from the landowner. Experience shows that most landowners will give permission and many are interested in the history of the mark and the hunt and will want to help you find it.
What do I do when I find a benchmark?
You simply log your find on the Geocaching.com site by clicking on "Log this benchmark" near the top right of a Geocaching.com benchmark datasheet. You NEVER EVER take them, even when they appear to have been damaged. These markers are public property, are actively used in surveying, and are protected by law. In the unlikely event that you discover a marker lying loose on the ground, the best thing is to leave it where you found it and contact the agency who is listed on it.
How do I know whether I've found the right benchmark?
Being sure you've found the right benchmark can sometimes be difficult and requires experience. The next 3 sections describe how to answer this question depending on the type of mark you're looking for.
Disks
If the datasheet says the designation of the disk you're looking for is CEDAR ...
  • If you found a disk that says: CEDAR then you have found the correct disk, even if it has a date with it, like CEDAR 1959.
  • If you found a disk that says: CEDAR RESET then you have not found the correct disk. Even if the disk is in the right place, it is not a find of station CEDAR.
  • If you found a disk that says: CEDAR RM1 then you have not found the correct disk. What you have found instead is a reference mark. Check the box score for CEDAR to find the azimuth and distance from it to CEDAR RM1. Reversing the azimuth will help you find the real station CEDAR.
  • If you found a disk that says: CEDAR AZ then you have not found the correct disk. This is the azimuth mark that is associated with station CEDAR but it is not station CEDAR.
  • If you found a disk that says: CEDAR 2 then you have not found the correct disk. Such a name usually means that the original station CEDAR was no longer findable or usable, and a new station was set nearby with a derivative name.
  • If you found a disk that has some other writing but not CEDAR, then you have not found the correct disk whether or not it is in exactly the right place.
The only reference marks and azimuth marks that can be logged on their own are those that have their own PID. If you're looking for a triangulation station and only find its reference mark or azimuth mark, you can't properly claim "Found it" (unless the reference mark or azimuth mark has its own unique PID, in which case you'd log it under that PID), but you could log it as "Couldn't find it" and even upload the picture of the reference mark.
Intersection Stations
Intersection stations are surprisingly tricky. Be sure to read the entire datasheet carefully. Pay particular attention to the first date the structure was reported or established as a survey mark (usually listed as the date "First Observed"). The structure you find must be one that you're certain existed and appeared the same way as it did on that date. If the structure was re-built then the station is effectively destroyed since the re-built version of the structure might be in a slightly different position. If you're uncertain about what happened during the time between when the structure was first monumented (observed) and the present, check with the structure's building manager. Since all intersection stations have adjusted coordinates, they must be at the published coordinates. If there is no such marker at the published coordinates, then the mark should be considered destroyed. If you find a structure that seems to be the correct one, but your GPS indicates that the position is incorrect, you have not found the correct mark.
If the intersection station is a water tower, read the datasheet carefully to note the details of the description of the water tower, and the first date the water tower was reported or established as a survey mark. For example, the datasheet says the water tower has 4 legs, has a cone shaped top, and was monumented in 1931.
  • If you found a water tower that has 6 legs or just one leg (a standpipe), then the water tower station has been replaced, and the water tower station described is destroyed.
  • If you found a water tower that looks newer than one built in 1931, then the water tower station has been replaced, and the water tower station described is destroyed.
  • If you found a water tower that has 5 legs and a round top, then the water tower station has been replaced, and the water tower station described is destroyed.
  • If you have found a water tower that is in the wrong coordinates, then it is not the correct water tower, even if it is what was described in the datasheet, because all water tower stations are location adjusted and cannot be at the wrong coordinates. You should go to the position of the datasheet's coordinates as indicated by your GPS receiver. If the correct water tower is not there, then the station is destroyed.
Other Kinds of Marks
Be sure to read the entire datasheet carefully. Sometimes an older type of mark will be replaced by a disk but the datasheet will still indicate the older type of mark in the Marker Type or MARKER field. If the type of mark has officially changed, the change will be noted in one of the recovery reports, and the new type described in that recovery report. If there is no change in the type of mark indicated in any of the recovery reports, you must not assume a change in the type of mark and it will be as in dicated in the Marker Type or MARKER field of the datasheet.
If you find a disk instead of the item described in the datasheet, you have not found the correct mark. In such a case, it is very likely that another agency who used to use the former mark has monumented a disk there. The disk is not a find. If you find a metal nail, rivet, spike, and it is not exactly what is described then you have not found the correct marker.
I am working on finding a triangulation station and its associated marks and I want to know how I can find the main station from the reference marks and vice versa?
Triangulation stations usually have reference marks associated with them. NGS recovery reports of triangulation stations involve looking not only for the principal mark, but also for any associated reference and azimth marks. Usually at least one of these is fairly obvious and that will give you a start on finding the others.
The measurements between the triangulation station and the reference marks are almost always given in what's called the box score. The box score gives the true North azimuth from the triangulation station to each reference mark in the format Degrees Minutes Seconds (dddmmss.s) but using just degrees part is sufficient for hunting. A Geocaching datasheet does not have the box score feature, but you can click on "view original datasheet" to see if the (circa 2000) NGS-format version has one.
It helps to have a compass that reads to the nearest degree, but the most precise thing you will be using is the tape measure, so depend mainly on it. Make arcs on the ground at the required distance if you can, so as to use the tape to the greatest advantage. The ideal is to have two out of the three marks found, and then you can use an intersection of measurements to find the third mark. Usually reference marks are more or less at right angles to each other with respect to the triangulation station.
If you're looking for a reference mark from the triangulation station, use the azimuth from the box score. On the other hand, if you're trying to find the triangulation station from a reference mark, you need to convert the azimuth to the opposite direction using the following simple rule: If the azimuth is less than 180 degrees, add 180 degrees, otherwise subtract 180 degrees.
Azimuths in a box score are in terms of true North. Your compass points to magnetic North instead. To convert from one to the other, you must get the declination and use it. The declination is different everywhere on Earth and changes as time goes by, so you will need the current local declination at the approximate position of the triangulation station. Declinations are either positive or negative. In order to follow the azimuth that the box score calls for, subtract the local declination from the box score's azimuth, then follow your compass with the resulting value. For example, if the declination is -10 and the box score's azimuth is 87 degrees toward a reference mark, then on your compass, look in the direction of 87 - (-10) = 97 degrees toward the reference mark.
NOAA's Declination Website can be used to determine the declination for a given location. You can also find the declination on a Topozone map. The declination value is below the bottom right corner of the map and is the value next to "M=".
Since you will probably be using a tape measured in feet, you must convert the metric distances in the box score from meters to feet. It's probably best to do that at home on your datasheets before going on your hunt. To convert, multiply the number of meters by 39.37 and divide the result by 12. Then, if your tape is feet-and-inches, multiply the decimal part of the last result by 12 to get the number of inches.
Here is another tip: If you are wanting to find an azimuth mark from a triangulation station, first get the azimuth and distance from the triangulation station to the azimuth mark from the datasheet's box score. Then use the GeoCalc or the FORWARD program to convert this data into the azimuth mark's coordinates. Even though a more accurate way to find the azimuth mark would be to tape along the azimuth, the amount of tape required and the insufficient precision of your compass makes it impractical for a non-surveyor. Before going out on your hunt, use one of these programs to generate the coordinates of the azimuth station and write them on your datasheet!

Logging Benchmarks

How do I log a benchmark?
On the benchmark's page, click on "Log this benchmark" at the top right corner of its page to log your find. After you have successfully logged your find, you can click on "upload images" to upload your pictures. When uploading images, you can put the station's Designation (name, not PID) as well as its State and location in the "Name:" field - it makes the benchmark gallery more interesting.
Logging Disks and Other Small Markers
If you have a digital camera, we ask that you take a closeup picture of the mark, and another picture from a few feet away, making sure that the mark is in the view. Additional pictures are OK too. Even if you don't have a digital camera, just log your find for others to read.
Triangulation Station Disks
A complete log for a triangulation station includes notes on not only the station itself, but also its reference marks and azimuth mark. If you don't look for them, please note that you didn't look for them. If you find them, include their pictures in your log. Also, include your GPS receiver's averaged coordinates for the azimuth mark.
Location-Scaled Disks
If you find a disk with a scaled location, please include your GPS receiver's averaged coordinates for the disk's location in your log (unless somebody else has already done so).
Logging Intersection Stations
Unless (in very unusual cases) the description says that there is a benchmark disk, surveying nail, or other small object that can't be seen from the ground, the top of the tower, steeple, or smokestack is the station. Do not climb it. Simply log your find, and if you have a digital camera, take the structure's picture from the ground.
What do the choices "Found It", "Didn't Find It", "Destroyed", and "Post a Note" mean?
  • You can log "Found it!" if you see the marker and know that it is the correct marker. If the marker is a survey disk, youmust read the disk. The designation (its name) stamped on it must match the Designation in the description. Reading the disk is necessary because another disk could have been set within a few feet of the one you're looking for. If the station has reference mark disks, they don't count as the find; you must find the station disk itself.
  • If you searched carefully, and could not find the marker, you should log "Didn't find it!" so that other benchmark hunters will know that the mark is going to be difficult or impossible to find. There is nothing wrong with doing a good job of looking and not finding the marker, since many of them are actually gone and many others are buried under dirt, asphalt, concrete, etc.
  • "Destroyed" means that you know that the benchmark cannot be in its original location because the structure it was on is gone. Don't log as destroyed unless you are absolutely 100% sure. If there is any doubt at all, it's best to refrain from using this option and let someone else have a chance at finding it. Remember, you can always seek advice from more experienced hunters by posting a message, which may enable you to increase your chances of success!
  • "Post a Note" is good for letting other benchmark hunters know about some special problem they may encounter looking for the benchmark, for an update on the benchmark's status, etc. Many experienced benchmark hunters use the "Post a Note" function to indicate that a benchmark is inaccessible (cannot be safely or legally searched for) because it is in a restricted area or on private property (and the owner withholds permission to access).
I looked for a disk in the place described in the datasheet but the disk is gone and only the stem remains. How should I log this?
This 'diskless stem' situation is a difficult one and requires a lot of experience to help you make sure you've found actual evidence of the mark you're looking for. The most obvious features are the brass metal stem and the circular evidence of a disk having been mounted there. Often there is a circular indentation that held the disk and some of the mounting cement might remain. These situations should be reported as "Found It" instead of "Destroyed" since the stem of the disk could possibly still be used for some types of surveying. If you're not really sure you've found the correct remains (more than one disk could've been mounted in the immediate area, there are many holes in cement but few of them are where benchmarks were), report your findings as accurately as you can and log "Didn't find it". In all cases of diskless stems, photographic evidence in your log is extremely helpful.
What are the most common errors in logging benchmarks?
The most common (representative) errors are:
  1. Mistaking a reference mark for a triangulation station and incorrectly logging "Found it" for the triangulation station even though they didn't find it.
  2. Logging as "Found it" a church steeple first observed in 1932, but the cornerstone on the church building says 1963 (the 1932 station is "Destroyed").
  3. Logging as "Destroyed" a survey disk whose position is now under the recently-added lane of a paved road (the disk may survive under the pavement; should be logged as "Didn't find it").
  4. Finding a disk stamped BITSKO RESET 1976 and logging as "Found it" a benchmark designated as BITSKO 1954 (BITSKO 1954 should be logged as "Didn't find it").
  5. Logging as "Found it" a water tank first observed in 1948 but whose location is occupied by a watershpere (there aren't any waterspheres in the database, the 1948 water tank is "Destroyed").
  6. Using "Post a Note" with the added explanation "Searched all over but could not find the disk" (should be logged as "Didn't find it").
  7. Being affected by a bias toward declaring "Found It". Don't let your interest in increasing your 'find count' adversely affect the accuracy of your logs. Someone else finding the correct marker, thereby proving that you made an error by logging the wrong item as a find is much more embarrassing than someone else finding a benchmark that you could not find.

Benchmarks Not in the Database

I found a benchmark, but it isn't in the database. Why?
To answer this question, you need to understand a bit about what "the database" is. The database used by Geocaching.com is a copy (from around 2000) of the database that NGS maintains. Although the NGS database has lots of marks in it, it does not have them all. In order for a mark to get into NGS's database, it has to go through a process known as "bluebooking" which ensures the disk meets the minimum requirements to be of geodetic quality (aka the highest quality possible). The NGS is not the only organization that creates and uses benchmarks and other types of control markers. In order for any mark to get "in the database" they must be "bluebooked", which can take a lot of time and effort and is often not done to save money. Remember, even though some marks might not be in the database, they are still highly important, both to businesses and to individual citizens such as your neighbors, so please treat them with respect, while enjoying the thrill of the hunt. We'll try to find other databases and add them to the site as well. If you have access to one of these databases and would like to submit it to Groundspeak, contact us.
Since the Groundspeak benchmark database was obtained from the NGS in the year 2000, newer benchmarks and recent reports on older marks will not be visible here in Groundspeak's copy. Besides new disks, there are many cases of benchmarks monumented significantly before 2000 but entered the NGS database only after the year 2000.
The benchmark I found is not in the database, how can I log it?
If the benchmark is a disk-type marker or is referenced in an online database, you can log your find in the US Benchmarks category in Groundspeak's Waymarking site.
If the benchmark is in Canada, you can log it in the Canadian Benchmarks category in Waymarking.
I found a U.S. Geological Survey bench mark where there is a "BM" mark on a topographic map, but it isn't in the database. Where can I find more information about this kind of mark and how can I log them?
The U.S. Geological survey (USGS) established thousands of benchmarks to help them make their topographic maps. The number next to the "BM" is the originally measured elevation of the disk. A large number of these USGS marks are not in the NGS database be cause they were never "bluebooked" as explained in the section above. The NGS and the USGS are separate government agencies so the inclusion of USGS marks in the NGS database is not automatic. Unfortunately the USGS did not get their paper records of benchmark location notes onto computer files. This makes those USGS marks that are not in the NGS database quite a challenge to find! You can log USGS disks you find that are not in the database in the US Benchmarks category in Groundspeak's Waymarking site.
How can I find out more about a benchmark that isn't in the database?
If you find a marker that isn't in the database, please do not email the Geocaching site or the NGS with the information. Instead, feel free to challenge your fellow hunters to help you identify any markers you find by posting in the Benchmark Hunting Forum. If you have logged your find in the US Benchmarks category, you can include a picture in your post by linking to the picture in that log.

Other Questions about Benchmarks

Why do the coordinates of some benchmarks seem to be way off?
The benchmarks that have inaccurate coordinates are always the "location scaled" benchmarks. The "location adjusted" benchmarks always have extremely accurate coordinates. See the above section called "What is the difference between"Location Adjusted" and "Location Scaled"?" and the next section called "How can I determine whether a particular mark is Location Adjusted or Location Scaled".
Can I log an official report to NGS?
Yes. NGS appreciates the efforts of geocachers and encourages them to submit reports on the condition of benchmarks. However, keep in mind that although we seek out benchmarks and report them for fun, the NGS database is in use by professionals for real world purposes. (They ask for your name and email address.) If you are interested in reporting to the NGS, please consider visiting the National Geodetic Survey forum. There you will find a FAQ topic that gives additional information on what is entailed in reporting to NGS.
Do we have an agency code for reporting to the NGS?
Yes, you can use the GEOCAC agency code for your report.
I'm interested in finding out more about benchmarks. Where can I get more information?
The good folks at the NGS have done an excellent job with their own Frequently Asked Questions Page. Check it out! The NGS also provides links to a large number of interesting articles on its on-line publications page. If you want to know all about the NGS database, check out its specifications section. The NGS has a fascinating page on the history of the NGS and its surveying and a new page on its 200 year anniversary. You can use the NGS search engines for finding control point datasheets (click on "Datasheets"). The NGS sample data sheet page is an excellent guidance for reading the datasheets.
Here are some links that you can use to find out more about benchmarks.
  • National Geodetic Survey (NGS) Maintainer of federal benchmark database. Includes various ways to retrieve up-to-date official datasheets.
  • Point of Beginning Online magazine for survey and geodesy professionals includes articles on current technology and history of the profession.
  • Berntsen International Leading manufacturer of benchmark disks and related products. A custom disk makes a fine gift.
  • Garmin, Magellan, Lowrance Major makers of handheld GPS receivers.
What are some softwares that benchmark hunters use?
  • BMGPX - this software converts an NGS .dat file into a .gpx file, a format that many softwares use.
  • EasyGPS - this software will read .loc and .gpx files, show a plot of the locations and send or receive location data between your computer and your GPS receiver.
  • GSAK (Geocaching Swiss Army Knife) - this software will read .loc and .gpx files, show a plot of the locations and send or receive location data between your computer and your GPS receiver, convert to .html files for PDAs, and handles numerous other waypoint management tasks.
  • Google Earth - Google Earth will read both .gpx and .loc files and display markers for them on its map.

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