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Details for Benchmark: AC7983

N 44° 04.188 W 103° 29.042 (NAD 83)

Altitude: 4641

Coordinates may not be exact. Altitude is GPS OBS and location is ADJUSTED. (more info)

Location:
In PENNINGTON county, SD View Original Datasheet
Designation:
SOUTH A B
Marker Type:
bench mark disk
Setting:
surrounded by a mass of concrete
Stability:
Mark of questionable or unknown stability.

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Found this one just north of the parking lot on the dam. The coordinates were right on.

[Photos:]
photoAC7983 / SOUTH AB / UNK
South AB and the GPS
photoAC7983 - SOUTH A B - AC7983
Looking south from the marker back toward the Visitors Center. The marker is to the right and just beyond the camera.

Found in good condition below the dam and visitor center parking lot.

[Photos:]
photoSOUTH A B - Pennington, SD
photoSOUTH A B - Pennington, SD
photoSOUTH A B - Pennington, SD

Found this after completing nearby "Alcatraz" cache. Marker is in very good condition.

[Photos:]
photoPactola/Alcatraz Area Marker
Pactola/Alcatraz Area Marker

Found this BM while hunting for the Alcatraz cache on Pactola Lake, Black Hills, SD.

[Photos:]
photoAC7983
photoAC7983
A view of Pactola Lake and the BM, Black Hills SD

Found it.

[Photos:]
photoAC7983 - SOUTH A B

Nice view of Pactola lake from this one.

The benchmark appears to be in great shape and the concrete base that it's set in hasn't moved. Picture attached.

[Photos:]
photoPactola Dam Benchmark AC7983

Documented History (by the NGS)

Unknown by (MONUMENTED)
03/12/1996 by SDDT (GOOD)
DESCRIBED BY SD DEPT OF TRANSP 1996 (DFC) THE STATION IS LOCATED ABOUT 16.0 MI (25.7 KM) WEST OF RAPID CITY, 14.0 MI (22.5 KM) NORTH/NORTHEAST OF HILL CITY, AND 5.0 MI (8.0 KM) SOUTHEAST OF SILVER CITY, AT THE PACTOLA LAKE VISITORS CENTER ON U.S. HIGHWAY 385. OWNERSHIP--U.S. DEPARTMENT OF AGRICULTURE. TO REACH THE STATION FROM THE POST OFFICE IN HILL CITY, GO NORTHEAST ON U.S. HIGHWAYS 385 AND 16 FOR 3.5 MI (5.6 KM) TO THE JUNCTION OF U.S. HIGHWAY 16 EAST AND U.S. HIGHWAY 385 NORTH, TURN LEFT AND GO NORTH ON U.S. HIGHWAY 385 FOR 10.0 MI (16.1 KM) TO THE PACTOLA LAKE VISITORS CENTER AND THE STATION ON THE LEFT. THE STATION IS LOCATED 100.0 FT (30.5 M) NORTH OF A CORNER OF THE NORTH GUARD RAIL, 75.0 FT (22.9 M) NORTHEAST OF THE NORTH END OF A METAL HANDRAIL, 75.0 FT (22.9 M) WEST OF THE HIGHWAY CENTER, 15.0 FT (4.6 M) BELOW THE LEVEL OF THE HIGHWAY, AND 2.0 FT (0.6 M) NORTHEAST OF A WITNESS POST.

Control Text

  • The horizontal coordinates were established by GPS observations and adjusted by the National Geodetic Survey in April 1997. This is a SPECIAL STATUS position. See SPECIAL STATUS under the DATUM ITEM on the data sheet items page.
  • The orthometric height was determined by GPS observations and a high-resolution geoid model.
  • The X, Y, and Z were computed from the position and the ellipsoidal ht.
  • The Laplace correction was computed from DEFLEC99 derived deflections.
  • The ellipsoidal height was determined by GPS observations and is referenced to NAD 83.
  • The geoid height was determined by GEOID99.

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