WELCOME TO MY BENCHMARK HUNTING WEBSITE                                                          

 BENCHMARK HUNTING, AND RECOVERIES

On the following pages you can see descriptions and pictures of the SURVEY POINTS ( BENCHMARKS )
I have recovered.

Included are :

 NGS Benchmarks -  National Geodetic Survey
MHD Benchmarks -  MassHighway Dept. Geodetic Control

USGS Benchmarks - U.S. Geological Survey
UNKNOWNS - I can not find information on them.

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Benchmark Hunting


A fun hobby that can be done with a camera, compass and a tape measure, or may expand to using
a whole range of specialized equipment ( GPS UNITS, METAL DETECTORS, LASER MEASURERS,
AND A VARIETY OF DIGGING, PROBING, AND CLEANING TOOLS )

The Datasheet for each mark contains the coordinates of the mark (precisely for Adjusted marks and roughly for Scaled ones), plus a narrative description of how to locate the mark in the field. Some of these descriptions are precise and correct, while others contain errors, refer to outdated landmarks, or are quite vague. The fun of the hunt consists of solving the "puzzle" of the directions to the mark, finding it (which may involve a bit of digging), and documenting your work with description and photos so that the next hunter to come along has an easier time than you did.

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 THE OLDEST SURVIVING SURVEY MARK  Station BUTTERMILK, located at the tip of the pen in this photo, was originally set in 1833 by Ferdinand Hassler. It is the oldest surviving triangulation survey mark in the United States. The other mark in the image was set in 1932, by the U.S. Geological Survey.

     

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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).

 Kinds of Benchmarks

 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.

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U.S. COAST & GEODETIC SURVEY - ( NOW NGS )
STANDARD DISKS

 




NATIONAL OCEAN SURVEY / NATIONAL GEODETIC SURVEY DISKS





 

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                                     DISKS IN THE VICINITY OF A U.S. COAST & GEODETIC SURVEY TRIANGULATION STATION

 

 Standard procedure for the USC&GS (and after the name change in 1970, the National Geodetic Survey) was to set four disks at ground surface level, a TRIANGULATION STATION disk (where the survey observations were made), two REFERENCE MARK disks, and one AZIMUTH MARK disk. Underground marks may also have been set, see details below.

 

TRIANGULATION STATION - A Triangulation Station is a survey point established during a survey utilizing the triangulation surveying method. Triangulation consists of observing the angles at the vertices of adjacent triangles, measuring the lengths of some sides, and computing the lengths of the remaining sides. The goal of this procedure is to determine the horizontal positions (latitude and longitude) of the vertices of each triangle (the points marked by TRIANGULATION STATION disks). The triangulation method thus produces accurate horizontal positions but only approximate elevations. Later, if a leveling survey crew was nearby, they may have leveled to one or more of the disks providing more accurate elevations.

 

The standard for many years was to set four disks at ground surface level in the vicinity of a Triangulation Station. However, there may be 6 or more survey disks in the vicinity, counting underground mark(s), additional reference mark(s), and mark(s) of other organizations. Note, other agencies may have used the same station name so care must be taken in identifying the correct agency’s survey disk. The main station, marked with a Triangulation Station disk, contains the factory stamping “TRIANGULATION STATION” with an equilateral triangle in the center. In addition, an underground mark may have been set about four feet beneath the surface. First the lower mark was set in a small mass on concrete, then a layer of dirt was added to isolate the lower mark, then the concrete monument was added, and then the surface mark was set directly over the underground mark. The underground marks were set to preserve the surface mark’s position if the surface mark was damaged or destroyed. Both disks contained the same factory stamping (“TRIANGULATION STATION”) and contain the exact same stamped designation (name) and date. Triangulation Stations were normally named for an area feature or for the property owner. Just prior to setting, the disk would be stamped by the original surveyor, for example, “JONES 1936”. In the NGS database, the name would be “JONES” and the year set 1936. The disk was usually set so that the stamping could be read by an observer facing north. The surface disk would be set in a concrete monument buried in the ground, or set in a drill-hole in a large structure or bedrock. The concrete monument is normally about flush with the ground’s surface, 12 inches in diameter, and 48 inches or more deep, with the bottom larger in diameter to help resist frost heave. The USC&GS TRIANGULATION STATION type of disks were used from about 1900 to about 1970 (although there were several different versions). After about 1970, National Geodetic Survey HORIZONTAL CONTROL MARK disks were used.

 

REFERENCE MARKS - Reference Marks (RM) were set to assist in locating the Triangulation Station and also to help determine if the Triangulation Station was undisturbed in its original position. The measured directions and distances to them could also be used to reset a station mark if required. Reference Marks were factory stamped with “REFERENCE MARK” and with an arrow used to point in the direction to the Triangulation station. The original surveyor stamped the RM with the name of the Triangulation Station plus the number of the RM, just prior to setting. For example, the first RM for station JONES would be stamped “JONES NO. 1 1936”. The surveyor measured the direction and distance from the triangulation station to the Reference Mark (RM) and recorded the information as part of the station’s description. Later, if a surveyor attempting to find a Triangulation Station stumbled upon a RM first, the arrow and the published distance and direction between the RM and station would be valuable aids in the station recovery. To check the position of the Triangulation Station, the new surveyor could measure the angles and distances to the Reference Marks and compare them to the original values. USC&GS specified a Reference Mark as early as 1913. By the 1920’s, two Reference Marks per Triangulation Station were specified. Reference Marks were usually set within 30 meters (one tape length) of the station. Reference marks were numbered clockwise from north and set about 90 degrees apart. If a RM was destroyed, a new Reference Mark would be set using the next consecutive number. The disks would be set in a concrete monument buried in the ground, or set in a drill-hole in a large structure or bedrock. This type of disk was used from about 1913 to about 1970. Although the distance and direction provided enough information to compute the positions of the RMs, it was not standard procedure to compute them. After about 1970, National Geodetic Survey REFERENCE MARK disks were used.

 

AZIMUTH MARKS – Beginning in 1927, a third Reference Mark, or long RM, was set about ¼ mile away from a station. They provided a starting azimuth (direction) for local surveys and for determining magnetic declination (difference between true north and magnetic north). Standard Azimuth Mark disks replaced azimuth reference marks about 1935. Also in 1935 the precision of the directions to Azimuth Marks was increased by changing the number of repetitions of the angle measurements from two to four. Azimuth Marks visible from the ground at the main triangulation station had been frequently requested by local surveyors and engineers. Azimuth Marks were factory stamped with “AZIMUTH MARK” and with an arrow. The original surveyor stamped the Triangulation Station’s name and date on the Azimuth Mark disk, just prior to setting. Since this is the exact same stamping as on the Triangulation Station disk, persons recovering the mark must check the factory stamping of “AZIMUTH MARK” (with arrow) versus “TRIANGULATION STATION” (with triangle) to determine which is which. When set, the surveyor rotated the Azimuth Mark disk until its arrow pointed directly toward the Triangulation Station disk. The surveyor then measured the direction, and in later years distance, to the Azimuth Mark (from the Triangulation Station) and recorded the information. Measuring the distance to the Azimuth Mark began in the mid 1970’s when electronic distance measuring equipment came into common usage, and underground marks were set at many of these. Azimuth Marks were usually set between ¼ mile and 2 miles from the Triangulation Station, at a location that was visible from tripod height at the Triangulation Station, and generally in or near a fence line along a road. The Azimuth Mark was included in the “To Reach” portion of the station’s description. The distance to most Azimuth Marks was measured with an odometer, so most don’t have adjusted positions and many are a challenge to recover. The disk would be set in a concrete monument buried in the ground, or set in a drill-hole in a large structure or bedrock. This type of disk was used from about 1935 to about 1970. After about 1970, National Geodetic Survey AZIMUTH MARK disks were used.

 

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