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Details for Benchmark: AE9189

N 41° 47.800 W 091° 38.550 (NAD 83)

Altitude: 714.89

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

Location:
In JOHNSON county, IA View Original Datasheet
Designation:
F 550.3
Marker Type:
bench mark disk
Setting:
set into the top of a metal pipe driven into the ground
Stability:
Mark of questionable or unknown stability.

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A wider search with the metal detector found it destroyed, about 8 ft from measured ties and lying horizontal just below the grass roots. Removed from area to prevent someone from creating confusion by putting it back in ground.

It is an aluminum pipe with the aluminum cap and point having shafts driven into the pipe and a rivet to retain the cap. Overall length is about 30 inches. It has magnets on the top of the spear point, but they are too deep to produce a distinctive response in a magnetic locator.

[Photos:]
photoAE9189-F550_3-1-20170704.jpg
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photoAE9189-F550_3-2-20170704.jpg
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photoAE9189-F550_3-3SW-20170704.jpg
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photoAE9189_Cap_Detail.jpg
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photoAE9189_Point_Detail.jpg
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Metal detector search and probing to 6 inches in area of coordinates and measured ties found no evidence of the disk. Flags indicate a fiber optic line has been added very near location, making it likely disk was destroyed.

Found in good condition. Witness post is gone. Handheld coordinates N41 47.784 W091 38.543. In the open but clearance above horizon may not meet standards.

Edit: Note that stamping is F-550.3 1986 not the 1980 monumented date on NGS data sheet.
Label on my picture is wrong - disk is South of the lake.

[Photos:]
photoAE9189_20040824_C.jpg
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Documented History (by the NGS)

01/01/1980 by USE (MONUMENTED)
01/08/1998 by NGS (GOOD)
DESCRIBED BY NATIONAL GEODETIC SURVEY 1998 (GAS) 1.3 KM (0.80 MI) NORTHWESTERLY ALONG NORTH DUBUQUE STREET FROM THE POST OFFICE IN NORTH LIBERTY, THENCE 5.3 KM (3.30 MI) NORTHERLY ALONG STATE HIGHWAY 965, 39.2 M (128.6 FT) SOUTHEAST OF A UTILITY POLE, 31.2 M (102.4 FT) NORTHEAST OF THE HIGHWAY CENTERLINE, 17.3 M (56.8 FT) NORTHEAST OF THE NORTHWEST END OF A CULVERT UNDER CURTIS BRIDGE ROAD, 13.9 M (45.6 FT) NORTHWEST OF THE ROAD CENTER, 1.0 M (3.3 FT) BELOW THE LEVEL OF THE HIGHWAY, AND 0.1 M (0.3 FT) NORTH OF A WITNESS POST. NOTE--THE DISK IS ENCASED IN A METAL PIPE AND IS FLUSH WITH THE GROUND SURFACE.

Control Text

  • 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 September 2000.
  • 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.

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