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Details for Benchmark: AA3904

N 41° 37.950 W 091° 32.450 (NAD 83)

Altitude: 648.6

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

Location:
In KEOKUK county, IA View Original Datasheet
Designation:
12 RESET
Marker Type:
vertical control disk
Setting:
setting not listed - see description
Stability:
Mark of questionable or unknown stability.

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As previously described and 28.7 ft east of a telephone pedestal, 24.5 ft SE of center of stump of large tree, 6 inches NW of witness sign, and 4 inches below surface at revised data sheet coordinates. Rail not visible.

Although the old elevation on this mark is bogus, it would make a good GPS location.

Found in good condition at handheld coordinates N41 10.610 W092 14.165, NGS and State Survey aluminum disk with a raised center, on a rod or pipe, stamped 12 RESET 1975. It is 3.4 miles east of Waldo St, which is the easternmost street of Hedrick and near the location of a former railroad line, 0.7 mile east of 5th street at the east side of Martinsburg, 205 feet west of the center of a driveway near address post 19108, on the south side of Highway 149 5.8 feet west of highway station post 485, about 125 feet northwest of a large metal building, 11 feet west of a rail set vertically and flush, 23.5 feet east southeast of a 2 foot tree, 6 inches north of a witness post, and 4 inches below the surface. Sky visibility would be good except for the one large tree.

Handheld GPS elevation 814 feet (NAD83). Mark is near the level of the highway. Topo map shows elevations between 800 and 850 feet in the general vicinity.

There is no longer a house nor a fence here. The disk is 10 feet west of a hole that could have held a corner post.

The listed coordinates are for MG0518 Designation 12 in Johnson county, near the Iowa City airport, and the listed elevation may be associated with that mark as it does not appear reasonable here. I have been unable to find a listing for the (destroyed) PID in Keokuk county of the mark it replaced.

NGS has changed the SCALED coordinates to my handheld values (rounded).

[This entry was edited by Bill93 on Tuesday, January 22, 2008 at 3:30:13 PM.]

[Photos:]
photoAA3904_20040913_A.jpg
photoAA3904_20040913_C.jpg

Documented History (by the NGS)

1/1/1975 by NGS (MONUMENTED)
DESCRIBED BY NATIONAL GEODETIC SURVEY 1975 (CLN) 3.3 MILES (5.3 KM) EAST ALONG STATE HIGHWAY 149 FROM THE RAILROAD CROSSING AND STATION IN HEDRICK, 136 FEET (41.5 M) WEST OF THE NORTHWEST CORNER OF MR KENNETH L HANDYS FARM HOME, 102.85 FEET (31.35 M) AND ON A LINE 15 DEGREES SOUTHWEST FROM THE ORIGINAL MARK, 10.5 FEET (3.2 M) WEST OF A RIGHT-OF-WAY RAIL AT A FENCE POST, 10 FEET (3.0 M) WEST OF A CORNER FENCE POST AND 6 INCHES NORTH OF A METAL WITNESS POST IN A FENCELINE, SET 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 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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