Details for Benchmark: JW1730
N 39° 42.100 W 079° 18.283 (NAD 83)
Coordinates may not be exact. Altitude is ADJUSTED and location is SCALED. (more info)
- In GARRETT county, MD View Original Datasheet
- SHA 230
- Marker Type:
- survey disk
- in rock outcrop
- Most reliable and expected to hold position/elevation well.
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Documented History (by the NGS)
|01/01/1992 by MDSHA (MONUMENTED)
|DESCRIBED BY MARYLAND DOT HIGHWAY ADMINISTRATION 1992
THE MARKER IS LOCATED ABOUT 3.0 MI (4.8 KM) WEST OF KEYSERS RIDGE, 5.1 MI (8.2 KM) NORTH OF ACCIDENT, AND 9.5 MI (15.3 KM) EAST-NORTHEAST OF THE MARYLAND-WEST VIRGINIA STATE LINE. IT IS LOCATED ON THE INTERSTATE HIGHWAY 68 RIGHT-OF-WAY. TO REACH FROM A POINT WHERE U.S. HIGHWAY 219 PASSES OVER INTERSTATE HIGHWAY 68 NEAR KEYSERS RIDGE, GO WEST ON INTERSTATE HIGHWAY 68 FOR 3.1 MI (5.0 KM) TO THE MARKER ON THE RIGHT. THE POINT IS MARKED WITH A MARYLAND STATE HIGHWAY ADMINISTRATION SURVEY DISK, CEMENTED IN A DRILL HOLE IN A OUTCROP OF BEDROCK. IT IS 48.5 FT (14.8 M) NORTHEAST OF THE CENTER OF THE WESTBOUND LANES OF INTERSTATE HIGHWAY 68, 3.0 FT (0.9 M) SOUTHWEST OF A CARSONITE WITNESS POST, 130.0 FT (39.6 M) NORTHWEST OF THE CENTER OF A DROP INLET, AND 410.0 FT (125.0 M) SOUTHEAST OF THE CENTER OF A BRIDGE NUMBERED 11047 WHERE PIGS EAR ROAD CROSSES OVER INTERSTATE HIGHWAY 68. IT IS ABOUT 7.5 FT (2.3 M) ABOVE THE SURFACE OF INTERSTATE HIGHWAY 68.
- The horizontal coordinates were scaled from a topographic map and have an estimated accuracy of +/- 6 seconds.
- The orthometric height was determined by differential leveling and adjusted by the National Geodetic Survey in April 1995.
- The geoid height was determined by GEOID99.
- The dynamic height is computed by dividing the NAVD 88 geopotential number by the normal gravity value computed on the Geodetic Reference System of 1980 (GRS 80) ellipsoid at 45 degrees latitude (g = 980.6199 gals.).
- The modeled gravity was interpolated from observed gravity values.