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If you spend any amount of time out hiking or biking you'll probably come across
one of these small metal discs in the middle of nowhere. It might say U.S. Coast & Geodetic Survey Benchmark, U.S Department Of Interior, Corp Of Engineers - U.S. Army, U.S. Geological Survey, Witness Corner or it might have a different legend. This page is a quick primer on what they are and how to use them. |
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This agency of the Federal Government, although virtually unknown outside of the government, is indeed one of the oldest agencies in our system of government. It was first established by President Thomas Jefferson in 1807 as the Survey of the Coast. As the American continent was progressively explored, inhabited and enclosed, the bureau took responsibility for survey of the interior. In 1878 it reorganized as the Coast and Geodetic Survey (C&GS). The National Geodetic Survey and the Office of Coast Survey are the two successor agencies in the United States to the U.S. Coast and Geodetic Survey. Since 1970, the National Geodetic Survey has been part of the National Oceanic and Atmospheric Administration within the United States Department of Commerce.
All across the continental US as well as in Alaska and Hawaii there is a network of survey monuments which are bronze disks about 8 to 10 cm. in diameter set in rock or permanent structures. The exact number can only be guessed at, but some estimates suggest that one million or more are in place in all manner of locations from city sidewalks and bridges to remote ridges and mountain tops. These have been set by surveyors since 1879 and are the basis for horizontal and vertical control for all the mapping done in the US. The survey monuments used for horizontal control are called triangulation stations, triangulation marks, control stations, or simply stations. A benchmark is a monument that is part of a leveling network and is a point of precisely measured elevation.
Looking at most any 7.5 minute or 15 minute topographic map you can probably find several benchmarks on it. Most of those at lower elevations are labelled with "BM" and an elevation next to an "X" mark. The ones of interest to the hiker, which are on high ridges or mountain tops, will be shown with a small triangle and most of the time an elevation is shown. There are some, maybe less than 5%, which will not have an elevation value. The name of the benchmark will be shown in a smaller type than the name of the summit. If the summit is unnamed then only the benchmark name will show. Many times the name of the benchmark is the same as the name of the mountain and is not shown separately.
| West Fork Trail (Greenbrier River, WV) | ||
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U.S. Coast & Geodetic Survey Benchmark K3 1933 Located on the Little River Bridge abutment. More information for this benchmark is here. |
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| Williams River Bridge | ||
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U.S. Coast & Geodetic Survey Benchmark For Information Write To The Director, Washington, D.C. K247 1962 |
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The bridge leads to the Tea Creek Campground. It is next to the Cranberry Wilderness. On this topo map you can see this benchmark indicated as BM 2968. Here is a link to the topo map on Terraserver. |
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| Blackwater River | ||
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U.S Department Of Interior Geological Survey Elev 3059 Ft 5/JEA 1964 Located on the Blackwater River Bridge, Blackwater Falls State Park, West Virginia. |
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On this topo map you can see this benchmark indicated as BM 3058. Here is a link to the topo map on Terraserver. |
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| Washington, D.C. | ||
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U.S Department Of Interior National Park Service 847HV00004 Located at the beginning of the C&O Canal. The marker is at the end of the stone pier. This pier was part of the canal's watergate. It's where the Watergate Hotel gets its name. The hotel is off picture to the left. In the background is The Lincoln Center and the Arlington Memorial Bridge. |
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| Dolly Sods | ||
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Corp Of Engineers - U.S. Army Survey Mark Dolly Sods 11 YEAR 1995 Located near the trailhead sign at Dolly Sods, above Laneville West Virginia. |
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| North Fork Blackwater River | ||
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WITNESS CORNER True Corner Bears N 07 37 10 W 66, 70 FT -1403L PS. NO. 359 2007 Located next to Douglas Road Outside Davis, West Virginia. |
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Witness Corner A witness
corner "stands in" when the true corner cannot be monumented or occupied because of difficult terrain or obstruction of the corner sight. The witness corner must be on the section line and is usually 5 or 10 chains away from the true corner. 7.92 inchs = 1 link 100 links in a chain or 66ft = 1 chain 10 chains = 1 furlong 80 chains = 1 mile | ||
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Here is another witness corner. It's obvious why you'd need a witness corner here. The arrow points off the edge of the cliff. |
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| North Fork Mountain | ||
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U.S. Geological Survey In Cooperation With The State Of West Virginia This marker is found at the top of Chimney Rocks on North Fork Mountain. |
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On this topographical map the marker can be found in the center. It is indicated by a triangle with the words "North Fork" and the elevation of 3553 (feet). Here is a link to the topo map on TerraServer. |
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This is the 360 degree view you will have while standing at this marker. |
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| Blackwater Canyon Trail | ||
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MONEL-METAL RIVET Monel-Metal is a nickel - copper alloy. This type of survey marker bears no legend of any kind. In the second photo you can see it embedded in the bridge abutment. |
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This marker is represented on the topo map as a "X" next to the elevation of "2781". Click here to go to on-line topo map. |
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To find the NGS Data Sheet for this type of marker requires a little extra work. go to the link for the TerraServer on-line topo map. By clicking on that point the web page gives the approximate longitude & latitude for the marker in decimal (39.12777,-79.51689). You need to convert that to degrees and minutes. Go to this FCC web page for the conversion. This returns latitude 39 degrees 7 minutes. Longitude 79 degress 31 minutes (ignore seconds). Looking at the all the entries on the NGS web page for Tucker County, WV there is only one entry that matches. The Designation is RV 26 and the PID is JW0860. From the NGS Data Sheet: JW0860 STATION DESCRIPTION JW0860 JW0860'DESCRIBED BY NATIONAL GEODETIC SURVEY 1935 JW0860'1.9 MI SW FROM THOMAS. JW0860'1.9 MILES SOUTHWEST ALONG THE WESTERN MARYLAND RAILWAY FROM THE JW0860'STATION AT THOMAS, TUCKER COUNTY, 0.2 MILE SOUTHEAST OF THE JW0860'DOUGLAS STATION, AT A STEEL BANNISTER BRIDGE OVER LONG RUN, IN JW0860'THE TOP OF THE SOUTHEAST WINGWALL OF THE SOUTH CONCRETE ABUTMENT, JW0860'27 FEET NORTHWEST OF A TOOL SHED, AND 12 FEET EAST OF THE JW0860'CENTERLINE OF THE TRACK. A STANDARD MONEL-METAL RIVET. |
| Blackwater Canyon Trail | ||
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AP-162 106I Buried down the center of Blackwater Canyon Trail are a series of these boundary markers. |
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Next to the trail are Bearing Trees that indicate the position of the buried boundary markers. |
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Each Bearing Tree has a metal plate and are carved and painted. |
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| Dolly Sods - Bear Rocks | ||
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2-911N PS842 1994 On the far ridgeline behind this sign for Bear Rocks Preserve. |
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The neat thing about this marker is that you can find the exact spot on the topographical map for the area. It's the corner of the National Forest boundary. I've highlighted it with an arrow. Here is a link to the topo map on Terraserver. |
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| 6.9 miles up the West Fork Trail is the Little River Bridge. |
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| South bridge abutment. the west (left) wing wall. |
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On the top of that wall is this Benchmark
Second picture is how that particular Benchmark is depicted on the Durbin WV 7.5 minute topographic map The number 2919 represents elevation. |
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The NGS keeps a data sheet accessable to the public for many, but not all benchmarks shown on the maps. These contain the name and location of the benchmark indicating the state, county, and USGS quad or topo map that it is on as well as precise survey data such as latitude, longitude, elevation and numerous other parameters mainly of interest to a surveyor. Along with the precise survey data is also a history section that often shows interesting information about the area since it must include detailed directions to the benchmark. To look up information about this example benchmark we need three pieces of information. The State (West Virginia), County (Pocahontas) and the Designation. The Designation is the name/date or letter-number/date stamped on the center of the disk. This disk has "K3" stamped over what looks to me like "1933". There are other ways to look up a benchmark but I find this way easiest. |
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So lets go to the NGS DATASHEET RETRIEVAL PAGE - BY COUNTY web page. Select "West Virginia" then click the "Get County List" button. |
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Under "Pick A County" select "Pocahontas".
Leave "Data Type Desired" and "Stability Desired" at the default settings. Leave the boxes unchecked. Click the "Get Marks" button. |
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This will bring up a list of all the benchmarks in
Pocahontas County. Look at the far right column in the list for Designations. Scroll down to select "K3". Then click the "Get Datasheets" button. |
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Actual Datasheet(Comments continue below) |
The NGS Data Sheet See file dsdata.txt for more information about the datasheet. DATABASE = Sybase ,PROGRAM = datasheet, VERSION = 7.42 1 National Geodetic Survey, Retrieval Date = FEBRUARY 14, 2007 HW1935 *********************************************************************** HW1935 DESIGNATION - K 3 HW1935 PID - HW1935 HW1935 STATE/COUNTY- WV/POCAHONTAS HW1935 USGS QUAD - DURBIN (1995) HW1935 HW1935 *CURRENT SURVEY CONTROL HW1935 ___________________________________________________________________ HW1935* NAD 83(1986)- 38 37 00. (N) 079 48 29. (W) SCALED HW1935* NAVD 88 - 889.537 (meters) 2918.42 (feet) POSTED HW1935 ___________________________________________________________________ HW1935 GEOID HEIGHT- -30.43 (meters) GEOID03 HW1935 DYNAMIC HT - 888.820 (meters) 2916.07 (feet) COMP HW1935 MODELED GRAV- 979,789.2 (mgal) NAVD 88 HW1935 HW1935 VERT ORDER - * POSTED, Code C , SEE BELOW HW1935 HW1935.The horizontal coordinates were scaled from a topographic map and have HW1935.an estimated accuracy of +/- 6 seconds. HW1935 HW1935.The orthometric height was determined by differential leveling HW1935.and adjusted by the National Geodetic Survey in 1992.. HW1935.* This is a POSTED BENCH MARK height. Code C indicates a distribution HW1935.rate of 2.1 thru 3.0 mm/km. HW1935 HW1935.The geoid height was determined by GEOID03. HW1935 HW1935.The dynamic height is computed by dividing the NAVD 88 HW1935.geopotential number by the normal gravity value computed on the HW1935.Geodetic Reference System of 1980 (GRS 80) ellipsoid at 45 HW1935.degrees latitude (g = 980.6199 gals.). HW1935 HW1935.The modeled gravity was interpolated from observed gravity values. HW1935 HW1935; North East Units Estimated Accuracy HW1935;SPC WV S - 180,100. 703,800. MT (+/- 180 meters Scaled) HW1935 HW1935 SUPERSEDED SURVEY CONTROL HW1935 HW1935 NGVD 29 (??/??/92) 889.611 (m) 2918.67 (f) ADJ UNCH 1 2 HW1935 HW1935.Superseded values are not recommended for survey control. HW1935.NGS no longer adjusts projects to the NAD 27 or NGVD 29 datums. HW1935.See file dsdata.txt to determine how the superseded data were derived. HW1935 HW1935_U.S. NATIONAL GRID SPATIAL ADDRESS: 17SPC037749(NAD 83) HW1935_MARKER: DB = BENCH MARK DISK HW1935_SETTING: 36 = SET IN A MASSIVE STRUCTURE HW1935_SP_SET: BRIDGE HW1935_STAMPING: K 3 1934 HW1935_STABILITY: B = PROBABLY HOLD POSITION/ELEVATION WELL HW1935 HW1935 HISTORY - Date Condition Report By HW1935 HISTORY - 1934 MONUMENTED CGS HW1935 HISTORY - 1983 MARK NOT FOUND NGS HW1935 HW1935 STATION DESCRIPTION HW1935 HW1935'DESCRIBED BY COAST AND GEODETIC SURVEY 1934 HW1935'7.4 MI N FROM DURBIN. HW1935'7.4 MILES NORTH ALONG THE WESTERN MARYLAND RAILWAY FROM THE UNION HW1935'STATION AT DURBIN, POCAHONTAS COUNTY, 0.2 MILE NORTH OF HW1935'MILEPOST E 40, AT A BRIDGE OVER GREENBRIER RIVER, IN THE TOP OF HW1935'THE SOUTH END OF THE WEST WING WALL OF THE SOUTH ABUTMENT, 4 HW1935'YARDS EAST OF THE CENTERLINE OF THE TRACK, AND ABOUT 1 FOOT HW1935'LOWER THAN THE TRACK. A STANDARD DISK, STAMPED K 3 1934. HW1935 HW1935 STATION RECOVERY (1983) HW1935 HW1935'RECOVERY NOTE BY NATIONAL GEODETIC SURVEY 1983 HW1935'MARK NOT FOUND. *** retrieval complete. Elapsed Time = 00:00:00 |
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Along the left of the datasheet is "HW1935". This is the PID of this Benchmark and it is a unique identifier. While the Designation "K3" might be used elsewhere, HW1935 will not. At the bottom of the Data Sheet is the part I find most informative. STATION DESCRIPTIONWhen the disc was set in 1934 this was part of the Western Maryland Railroad. It lists this point as 7.4 miles from the Durbin Station. Since I list it as trail mile 6.9 that means what I call the start of the trail is .5 mile from the station. This point is .2 north of (now missing) milepost 40. The information is not infallible. It list this as a bridge across the Greenbrier River when actually it's across the Little River. Another problem is that it reads the disk was stamped "K 3 1934". I've gone back and checked it after reading this and I still think it's stamped "1933" Check out the final comment from 1983. "Mark Not Found". Strange, I found it without a problem. It's right where they left it. |
STATION DESCRIPTION
DESCRIBED BY COAST AND GEODETIC SURVEY 1934
7.4 MI N FROM DURBIN.
7.4 MILES NORTH ALONG THE WESTERN MARYLAND RAILWAY FROM THE UNION
STATION AT DURBIN, POCAHONTAS COUNTY, 0.2 MILE NORTH OF
MILEPOST E 40, AT A BRIDGE OVER GREENBRIER RIVER, IN THE TOP OF
THE SOUTH END OF THE WEST WING WALL OF THE SOUTH ABUTMENT, 4
YARDS EAST OF THE CENTERLINE OF THE TRACK, AND ABOUT 1 FOOT
LOWER THAN THE TRACK. A STANDARD DISK, STAMPED K 3 1934.
STATION RECOVERY (1983)
RECOVERY NOTE BY NATIONAL GEODETIC SURVEY 1983
MARK NOT FOUND.
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