Hi -- I read and liked your article on survey monuments. I'm a professional land surveyor who specializes in control surveying using the type of 'monuments' you show in your very fine article. I do have a couple of clarifications that I would like to add.
A 'benchmark' is a known monument of elevation, typically determined through a process called 'geodetic leveling' or just 'leveling'. 'Geodetic leveling' is a very precise measurement system that is very time-consuming (expensive) and is typically done along railroad grades, roads, and highways. These types of surveys typically aren't done on mountaintops, but of course there are always exceptions.
Most of the 'marks' (another word for 'monuments') shown in your article are associated with 'triangulation' stations. Normally, at least two 'reference marks' will be set somewhere nearby (under 100' and at 90-degrees to one another) that 'witness' the primary 'station mark'. These 'reference marks' were used by surveyors in case the 'triangulation station' was destroyed. USC&GS normally set underground marks (when practical) to perpetuate the station. Also, there will typically be an 'azimuth mark' set a couple thousand feet away so a surveyor can orient his/her survey to a known 'backsight'. Sometimes, these 'azimuth marks' are other 'triangulation stations' on other mountaintops.
Marks atop most mountains were classically determined through a measurement process called 'triangulation' whereby a measured line (base line) has a known length and position at each end of the line, then using trigonometry (actually, spherical trigonometry because the Earth is round) the unknowns are solved.
Elevations at 'triangulation stations' were classically determined using the 'vertical angles' determined by the surveying instrument (called a theodolite), and wasn't nearly as precise as 'geodetic leveling' -- nor did it have to be. Generally, the elevations of triangulation stations only needed to be within 10-20 feet or so, because this was a factor (computationally) in determining horizontal positions, which was the main purpose of 'triangulation'.
Classical 'triangulation' is a very expensive method of survey measurement and is not performed any longer. It has been replaced by much more precise centimeter-level GPS surveys, which don't require line of sight like triangulation. Its also much faster (less expensive) than triangulation. Its a matter of economics and practicality at this point in the surveying profession -- cost is the primary reason why these older triangulation stations on mountain tops aren't surveyed any longer.
As you point out in your article, there was a clear division of labor between the USGS who did topographic mapping and USC&GS/NGS who was responsible for the vast majority of geodetic surveys in the United States. USC&GS/NGS used very specific 'monuments' for specific purposes, whether it was a 'benchmark' surveyed using 'geodetic leveling' techniques or a 'triangulation station' determined using that technique. USGS typically used one monument type ('benchmark' or 'BM') for all their work. USGS typically doesn't perform field work any longer for their topographic mapping, but they are involved in scientific studies of Earth movement in various parts of the United States. One might see USGS marks in California (GPS surveys for earthquake studies) or at the rim of volcanoes in Hawaii, (geodetic leveling surveys for monitoring). In a nutshell, USGS uses a generic 'monument' type for all its surveys, with 'benchmark' or 'BM' embossed on the 'monument'. On the other hand, USC&GS/NGS uses 'monuments' embossed with a specific purpose in mind such as 'traverse station', 'triangulation station' (classical horizontal control), 'benchmark' (classical vertical control), etc. There are also other NGS 'monument' types that you will see if you look hard enough around major universities and airports -- 'magnetic stations' and 'gravity stations'.
The cadastral monuments you show in your article are unique to the United States public lands survey system (section, township, and range). These are only found in the west of the original thirteen colonies.
I trust this clarifies. For a guy who isn't a surveyor you did a great job -- I'm impressed. Keep up the good work and keep writing those articles!!!
Many mountain stations were established for horizontal control (triangulation) rather than for vertical control (benchmarks) and many of the marker descriptions indicate the elevation as being scaled rather than accurately measured. The precise elevation of a peak is really of little interest to the government so we should not be surprised if they don't bother to determine them more accurately.
Many peaks were named looking from below and the point seen may well have been an outcrop rather than the highest point which may be a flattish spot set back. Similarly, the survey point was probably set not to measure the highest elevation but rather as highly visible from a distance or the best spot nearby to set up an instrument. So the survey point may well not be the highest point and the named point may not be the highest point either - Mount Wood may be the W point even though the E point is higher.
The Smoky Mountains National Park has sent out volunteers with industrial-strength GPS's to do elevation surveys of the peaks within the Park. With a good view of the sky, accuracies of inches is possible. With the GPS data one can compare to older survey results and recent LiDAR surveys. Preliminary elevation survey results are here:
Well, that's a start. Results look reasonable too. I'm sure there are a bunch of folks out there who would volunteer to do this in other areas. Aside from NPs supporting this effort inside their boundaries, I wonder which agencies would support this on other peaks...
We have all seen benchmarks, but you are right--none of us have been stirred to research them as you have done. Great work, totally appreciate the effort you have made. 10/10
Dad was a USGS field topographer from the early 1950's until they reassigned him to the western division office in about 1985. He passed away in 2014. The western division was the seven western states, WA, ID, OR, CA, NV, UT and AZ. We usually moved twice a year, north in the summer, south in the winter and generally lived in the smallest of towns. As a kid I sometimes helped him lug theodolites to the tops of peaks and have helped place benchmarks.
If the benchmark isn't on the highest point, it may be due to accessibility but more likely visibility. The more peaks you can see from a summit, the more important it is for triangulation. The benchmark doesn't mark a significant feature but a reference point in the triangulation grid. They are generally on peaks because you can generally see more from there.
I've been reading up on surveying, and trying to understand the names, rhymes, and reason around the various survey mark disks. So I enjoyed your article. I appreciate all the work you put into it.
As I read more and more on this topic I find again and again that the terms are not defined hard and fast. Which makes it confusing. Some of it might just be a matter of terms being used colloquially in one situation and formally in another.
For example, you define a bench mark like this "A bench mark is simply a reference point on a stationary object for which the geographic location (and usually elevation) is known, marked in some fashion to permit a surveyor to return to a location or create a new known location with a high degree of confidence."
My reading disagree with that description and cause me to believe "a bench mark is a point of precisely measured elevation". What you describe is what my reading call a horizontal control station. If the mark only has a known lat/long it is a horizontal control station, but if that same mark has a precisely measured elevation then it can also be called a bench mark. Also are you sure survey marks are set or made for the purpose of a surveyor being able to return to a location? Reference and long range reference marks (aka Azimuth Marks) are set to help the surveyor find a primary station, but primary horizontal control marks are not set for that reason.
When you state "..or create a new known location with a high degree of confidence" are you meaning "create an ADDITIONAL location"?
Here is what my other reading seem to agree on: A primary survey mark is a point on the earth for which an accurately measured location, either horizontally or vertically has been determined. Additionally other survey marks (non-primary) are disks which point to a primary mark, and these are known as Reference Marks. Both types of marks use the same sized disks, made of either bronze or aluminum, and stamped with text, numbers, and a symbol.
Vertical control marks are those for which a measured accurate elevation above sea level has been determined, and they are stamped at the center with a crossed slash symbol. Disks stamped with an equilateral triangle symbol in the center are horizontal control marks and they pinpoint a spot for which the latitude and longitude has been accurately calculated. Reference Marks are stamped in the center with a crossed arrow symbol, and are always set with their arrow symbol accurately pointing toward a primary mark.
Survey marks are known by various other names, such as monuments, points, bench marks, and stations. These names might also be proceeded with terms like survey, horizontal control, control, or triangulation – as in “triangulation station”. There are technical reasons for these names, but surveying is a complex discipline and terms end up being used interchangeably even if not strictly correct. For example, a bench mark is a point of precisely measured elevation, but some might call a monument concerned only with horizontal positioning a bench mark since they are both marked with metal disks. Whereas technically monuments concerned only with horizontal positioning are called horizontal control stations or simply control stations. A Triangulation Station is a specific type of a control station having had its position determined by measuring distances and angles from other stations. An Azimuth Mark is a long Reference Mark. Unlike a normal Reference Mark which is typically located within thirty meters (one tape length) of the primary mark, Azimuth Marks are set typically between one quarter of a mile and two miles from the primary mark, give or take.
Reference Marks, including Azimuth Marks, serve two purposes. First they provide a point from which a surveyor can locate a primary mark. Once the primary mark is found and the surveyor sets up his gear in order to make accurate measurements he needs a known point of reference, and that then is the second function of both types of Reference Marks – they allow the surveyor to know the exact direction in which he is looking.
One more point worth noting. Survey Disk are not typically concerned with being place on the highest point. They are set so as to be visible which means often they are at, on, or near the highest point which ever is the most visible.
I've often wondered why topi maps and sites like peakbagger.com don't use the nadv 88 elevations. I recently summited Kings Peak in Utah and my buddy (who was also my guide on this trip) mentioned that prior to about 1970, the south peak was thought to be the highest point in Utah, but now 5he north peak is regarded as being higher. Great article. Thanks for sharing!
Survey1989 - Mar 4, 2011 12:04 am - Voted 10/10
Good article overallHi -- I read and liked your article on survey monuments. I'm a professional land surveyor who specializes in control surveying using the type of 'monuments' you show in your very fine article. I do have a couple of clarifications that I would like to add.
A 'benchmark' is a known monument of elevation, typically determined through a process called 'geodetic leveling' or just 'leveling'. 'Geodetic leveling' is a very precise measurement system that is very time-consuming (expensive) and is typically done along railroad grades, roads, and highways. These types of surveys typically aren't done on mountaintops, but of course there are always exceptions.
Most of the 'marks' (another word for 'monuments') shown in your article are associated with 'triangulation' stations. Normally, at least two 'reference marks' will be set somewhere nearby (under 100' and at 90-degrees to one another) that 'witness' the primary 'station mark'. These 'reference marks' were used by surveyors in case the 'triangulation station' was destroyed. USC&GS normally set underground marks (when practical) to perpetuate the station. Also, there will typically be an 'azimuth mark' set a couple thousand feet away so a surveyor can orient his/her survey to a known 'backsight'. Sometimes, these 'azimuth marks' are other 'triangulation stations' on other mountaintops.
Marks atop most mountains were classically determined through a measurement process called 'triangulation' whereby a measured line (base line) has a known length and position at each end of the line, then using trigonometry (actually, spherical trigonometry because the Earth is round) the unknowns are solved.
Elevations at 'triangulation stations' were classically determined using the 'vertical angles' determined by the surveying instrument (called a theodolite), and wasn't nearly as precise as 'geodetic leveling' -- nor did it have to be. Generally, the elevations of triangulation stations only needed to be within 10-20 feet or so, because this was a factor (computationally) in determining horizontal positions, which was the main purpose of 'triangulation'.
Classical 'triangulation' is a very expensive method of survey measurement and is not performed any longer. It has been replaced by much more precise centimeter-level GPS surveys, which don't require line of sight like triangulation. Its also much faster (less expensive) than triangulation. Its a matter of economics and practicality at this point in the surveying profession -- cost is the primary reason why these older triangulation stations on mountain tops aren't surveyed any longer.
As you point out in your article, there was a clear division of labor between the USGS who did topographic mapping and USC&GS/NGS who was responsible for the vast majority of geodetic surveys in the United States. USC&GS/NGS used very specific 'monuments' for specific purposes, whether it was a 'benchmark' surveyed using 'geodetic leveling' techniques or a 'triangulation station' determined using that technique. USGS typically used one monument type ('benchmark' or 'BM') for all their work. USGS typically doesn't perform field work any longer for their topographic mapping, but they are involved in scientific studies of Earth movement in various parts of the United States. One might see USGS marks in California (GPS surveys for earthquake studies) or at the rim of volcanoes in Hawaii, (geodetic leveling surveys for monitoring). In a nutshell, USGS uses a generic 'monument' type for all its surveys, with 'benchmark' or 'BM' embossed on the 'monument'. On the other hand, USC&GS/NGS uses 'monuments' embossed with a specific purpose in mind such as 'traverse station', 'triangulation station' (classical horizontal control), 'benchmark' (classical vertical control), etc. There are also other NGS 'monument' types that you will see if you look hard enough around major universities and airports -- 'magnetic stations' and 'gravity stations'.
The cadastral monuments you show in your article are unique to the United States public lands survey system (section, township, and range). These are only found in the west of the original thirteen colonies.
I trust this clarifies. For a guy who isn't a surveyor you did a great job -- I'm impressed. Keep up the good work and keep writing those articles!!!
royswkr - Nov 4, 2011 10:25 am - Hasn't voted
be sure to read reply 22Many mountain stations were established for horizontal control (triangulation) rather than for vertical control (benchmarks) and many of the marker descriptions indicate the elevation as being scaled rather than accurately measured. The precise elevation of a peak is really of little interest to the government so we should not be surprised if they don't bother to determine them more accurately.
Many peaks were named looking from below and the point seen may well have been an outcrop rather than the highest point which may be a flattish spot set back. Similarly, the survey point was probably set not to measure the highest elevation but rather as highly visible from a distance or the best spot nearby to set up an instrument. So the survey point may well not be the highest point and the named point may not be the highest point either - Mount Wood may be the W point even though the E point is higher.
manitou - Dec 7, 2011 11:56 am - Hasn't voted
smoky mountain gps elevation surveyThe Smoky Mountains National Park has sent out volunteers with industrial-strength GPS's to do elevation surveys of the peaks within the Park. With a good view of the sky, accuracies of inches is possible. With the GPS data one can compare to older survey results and recent LiDAR surveys. Preliminary elevation survey results are here:
http://web.eecs.utk.edu/~dunigan/gsmnp/peaksgps.html
peakhugger - Dec 8, 2011 12:42 pm - Hasn't voted
Re: smoky mountain gps elevation surveyWell, that's a start. Results look reasonable too. I'm sure there are a bunch of folks out there who would volunteer to do this in other areas. Aside from NPs supporting this effort inside their boundaries, I wonder which agencies would support this on other peaks...
JoelSkok - Jan 7, 2019 11:03 am - Voted 10/10
NO, you are not going out on a limb by any means!We have all seen benchmarks, but you are right--none of us have been stirred to research them as you have done. Great work, totally appreciate the effort you have made. 10/10
danmerrick - Jan 24, 2019 5:41 pm - Hasn't voted
I'm a USGS "survey kid'Dad was a USGS field topographer from the early 1950's until they reassigned him to the western division office in about 1985. He passed away in 2014. The western division was the seven western states, WA, ID, OR, CA, NV, UT and AZ. We usually moved twice a year, north in the summer, south in the winter and generally lived in the smallest of towns. As a kid I sometimes helped him lug theodolites to the tops of peaks and have helped place benchmarks.
If the benchmark isn't on the highest point, it may be due to accessibility but more likely visibility. The more peaks you can see from a summit, the more important it is for triangulation. The benchmark doesn't mark a significant feature but a reference point in the triangulation grid. They are generally on peaks because you can generally see more from there.
vanman798 - Nov 22, 2020 12:22 pm - Hasn't voted
Definition...I've been reading up on surveying, and trying to understand the names, rhymes, and reason around the various survey mark disks. So I enjoyed your article. I appreciate all the work you put into it.
As I read more and more on this topic I find again and again that the terms are not defined hard and fast. Which makes it confusing. Some of it might just be a matter of terms being used colloquially in one situation and formally in another.
For example, you define a bench mark like this "A bench mark is simply a reference point on a stationary object for which the geographic location (and usually elevation) is known, marked in some fashion to permit a surveyor to return to a location or create a new known location with a high degree of confidence."
My reading disagree with that description and cause me to believe "a bench mark is a point of precisely measured elevation". What you describe is what my reading call a horizontal control station. If the mark only has a known lat/long it is a horizontal control station, but if that same mark has a precisely measured elevation then it can also be called a bench mark. Also are you sure survey marks are set or made for the purpose of a surveyor being able to return to a location? Reference and long range reference marks (aka Azimuth Marks) are set to help the surveyor find a primary station, but primary horizontal control marks are not set for that reason.
When you state "..or create a new known location with a high degree of confidence" are you meaning "create an ADDITIONAL location"?
Here is what my other reading seem to agree on: A primary survey mark is a point on the earth for which an accurately measured location, either horizontally or vertically has been determined. Additionally other survey marks (non-primary) are disks which point to a primary mark, and these are known as Reference Marks. Both types of marks use the same sized disks, made of either bronze or aluminum, and stamped with text, numbers, and a symbol.
Vertical control marks are those for which a measured accurate elevation above sea level has been determined, and they are stamped at the center with a crossed slash symbol. Disks stamped with an equilateral triangle symbol in the center are horizontal control marks and they pinpoint a spot for which the latitude and longitude has been accurately calculated. Reference Marks are stamped in the center with a crossed arrow symbol, and are always set with their arrow symbol accurately pointing toward a primary mark.
Survey marks are known by various other names, such as monuments, points, bench marks, and stations. These names might also be proceeded with terms like survey, horizontal control, control, or triangulation – as in “triangulation station”. There are technical reasons for these names, but surveying is a complex discipline and terms end up being used interchangeably even if not strictly correct. For example, a bench mark is a point of precisely measured elevation, but some might call a monument concerned only with horizontal positioning a bench mark since they are both marked with metal disks. Whereas technically monuments concerned only with horizontal positioning are called horizontal control stations or simply control stations. A Triangulation Station is a specific type of a control station having had its position determined by measuring distances and angles from other stations. An Azimuth Mark is a long Reference Mark. Unlike a normal Reference Mark which is typically located within thirty meters (one tape length) of the primary mark, Azimuth Marks are set typically between one quarter of a mile and two miles from the primary mark, give or take.
Reference Marks, including Azimuth Marks, serve two purposes. First they provide a point from which a surveyor can locate a primary mark. Once the primary mark is found and the surveyor sets up his gear in order to make accurate measurements he needs a known point of reference, and that then is the second function of both types of Reference Marks – they allow the surveyor to know the exact direction in which he is looking.
One more point worth noting. Survey Disk are not typically concerned with being place on the highest point. They are set so as to be visible which means often they are at, on, or near the highest point which ever is the most visible.
BubbaJuice - Oct 15, 2022 4:19 pm - Hasn't voted
CorrectionBenchmarks from the USGS appeared as early as 1896.
See:
https://geologistsofjacksonhole.org/wp-content/uploads/2016/11/The-1899-USGS-Grand-Teton-Quad.compressed.pdf pg.28
http://www.penryfamily.com/surveying/usgsosgood.html
https://wyofile.com/wyoming-monument-middle-nowhere/
Timpanogos Tom - Aug 22, 2023 7:05 pm - Voted 10/10
Great info on a topic I've often thought about!I've often wondered why topi maps and sites like peakbagger.com don't use the nadv 88 elevations. I recently summited Kings Peak in Utah and my buddy (who was also my guide on this trip) mentioned that prior to about 1970, the south peak was thought to be the highest point in Utah, but now 5he north peak is regarded as being higher. Great article. Thanks for sharing!