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Details for Benchmark: MG0518

N 41° 37.950 W 091° 32.450 (NAD 83)

Altitude: 649.25

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

Location:
In JOHNSON county, IA View Original Datasheet
Designation:
12
Marker Type:
NGS Benchmark
Setting:
setting not listed - see description
Stability:
Mark of questionable or unknown stability.

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This piece of "Old 218" is Hwy 921 or South Riverside Dr. The coordinates and description indicate a readily identifiable culvert near the Iowa City airport. The road has likely been widened since 1964 so the old headwall could be buried under the road or removed.

[This entry was edited by Bill93 on Saturday, September 18, 2004 at 10:21:46 AM.]

Documented History (by the NGS)

Unknown by IOWAGS (MONUMENTED)
1/1/1948 by IAHD (GOOD)
DESCRIBED BY IOWA HIGHWAY DEPARTMENT 1948 1.1 MI S FROM IOWA CITY. 1.1 MILES SOUTH ALONG U.S. HIGHWAY 218 FROM THE INTERSECTION OF STATE HIGHWAY 1 AT IOWA CITY, JOHNSON COUNTY, NEAR THE NORTHEAST CORNER OF THE SOUTHEAST QUARTER OF SEC. 21, T. 79 N., R. 6 W., AT PAVEMENT STATION 51+34, AT A 12-FOOT-WIDE CONCRETE CULVERT, AND IN THE TOP OF THE WEST HEAD WALL. A REINFORCING BAR.
1/1/1964 by NGS (GOOD)
RECOVERY NOTE BY NATIONAL GEODETIC SURVEY 1964 RECOVERED IN GOOD CONDITION.
1/6/1998 by NGS (MARK NOT FOUND)
RECOVERY NOTE BY NATIONAL GEODETIC SURVEY 1998 (GAS) THE HEADWALL HAS BEEN REPLACED. ASSUMED DESTROYED.

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 June 1991.
  • 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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