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Details for Benchmark: JV3975

N 39° 00.383 W 077° 15.267 (NAD 83)

Altitude: 159.9

Coordinates may not be exact. Altitude is VERTCON and location is SCALED. (more info)

Location:
In FAIRFAX county, VA View Original Datasheet
Designation:
V 157=DAM
Marker Type:
survey disk
Setting:
in rock outcrop
Stability:
Most reliable and expected to hold position/elevation well.

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Found as described by difficult run. Wish I had noticed his coordinates right away. They were excellent. It would be hard to miss this benchmark right along the trail.

Found this by accident. Was looking nearby for a letterbox hybrid cache and snapped a few pics just in case this disc was what I thought it was. Yay me. Didn't find the cache, but found the benchmark!

[Photos:]
photoJV3975 from a distance
Where I was looking...
photoJV3975 up close
... and this is what I found.

Found in good condition
Averaged coordinates: N39 00.410 W77 15.278
Area as described by Difficult Run.

[Photos:]
photoV 157=DAM In FAIRFAX county, VA (closeup)
photoV 157=DAM In FAIRFAX county, VA (area)
walking stick points to mark
N 39° 00.408 W 077° 15.277

Mark found in good condition.

Addition to datasheet is as follows:
Station set in a very large rock outcrop, roughly 40 feet NNE from the edge of a concrete sewage structure, about 30 feet east of the Potomac Heritage Trail and approximately 10 feet above the level of the aqueduct dam.

Disk shows signs of attempted vandalism from many years ago, but disk is still solid.

GPS coords are:
N39° 00' 24.5" W77° 15' 16.6" (DMS)

[Photos:]
photoV157 - Dam - Closeup1
photoV157 - Dam - Closeup2
photoV157 - Dam - Overview
Red Arrow points to benchmark. Washington Aqueduct Dam in Background.

Looked at nearly all the rock outcroppings in this area. No benchmark found. There are a few outcroppings on the shore which are covered with soil and plants, but I did not want to disturb them.

Did find a possible, but unlikely mark - see photos.

[Photos:]
photoV157_DAM.jpg
photoView From Hole in Rock

Documented History (by the NGS)

Unknown by PBPP (MONUMENTED)
01/01/1931 by (GOOD)
DESCRIBED 1931 6.4 MI W FROM LANGLEY. 6.4 MILES WEST ALONG STATE HIGHWAY 193 FROM THE METHODIST CHURCH AT LANGLEY, FAIRFAX COUNTY, THENCE ABOUT 1 MILE NORTH ALONG SECONDARY STATE HIGHWAY 738 (ON THE OLD WASHINGTON AND OLD DOMINION RAILROAD GRADE) TO GREAT FALLS PARK, AND THENCE ABOUT 1 MILE NORTH ALONG A TRAIL FOLLOWING THE WEST BANK OF POTOMAC RIVER, 50 YARDS SOUTH OF THE WASHINGTON WATER-SUPPLY DAM, AND IN THE TOP OF A ROCK OUTCROP. A PUBLIC BUILDINGS AND PUBLIC PARKS STANDARD DISK.
01/01/1959 by USGS (MARK NOT FOUND)
RECOVERY NOTE BY US GEOLOGICAL SURVEY 1959 MARK NOT FOUND.

Control Text

  • The horizontal coordinates were scaled from a topographic map and have an estimated accuracy of +/- 6 seconds.
  • The NAVD 88 height was computed by applying the VERTCON shift value to the NGVD 29 height (displayed under SUPERSEDED SURVEY CONTROL.) The vertical order pertains to the superseded datum.
  • The geoid height was determined by GEOID99.

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