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Details for Benchmark: HT1518

N 37° 12.900 W 122° 24.333 (NAD 83)

Altitude: 45.03

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

Location:
In SAN MATEO county, CA View Original Datasheet
Designation:
A 212
Marker Type:
bench mark disk
Setting:
massive structures
Stability:
Probably hold position/elevation well.

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The challenge was figuring out how to get to it.

[Photos:]
photoMarker

The headwall in the description is on the old, overgrown road to the east of Hwy 1. Found the remains of the headwall after trudging through vegetation (and quite possibly poison oak - always an adventure ). Benchmark still intact and in good condition.

[Photos:]
photoHT1518.JPG
photoHT1518 Location.JPG

Documented History (by the NGS)

01/01/1935 by CGS (MONUMENTED)
01/01/1972 by NGS (GOOD)
DESCRIBED BY NATIONAL GEODETIC SURVEY 1972 18.8 MI NW FROM DAVENPORT. 18.85 MILES NORTHWEST ALONG STATE HIGHWAY 1 FROM THE POST OFFICE AT DAVENPORT, AT THE CROSSING OF A POWER LINE, DIRECTLY ACROSS THE HIGHWAY FROM A TWO STORY HOUSE, IN THE TOP OF THE CENTER OF THE NORTHWEST CONCRETE WING WALL OF A BRIDGE UNDER THE FORMER HIGHWAY, 13 FEET WEST OF THE CENTER LINE OF THE FORMER HIGHWAY, 95 FEET EAST OF THE CENTER LINE OF THE HIGHWAY, 57 FEET EAST OF THE NORTH END OF THE EAST CONCRETE HEAD WALL OF CULVERT 10/35, 1.0 FOOT NORTHWEST OF THE NORTHWEST END OF A CONCRETE GUARDRAIL, 1.0 FOOT SOUTHEAST OF THE NORTHWEST END OF THE WING WALL, ABOUT LEVEL WITH THE FORMER HIGHWAY, AND 10 FEET LOWER THAN THE NEW HIGHWAY.
01/01/1978 by NGS (GOOD)
RECOVERY NOTE BY NATIONAL GEODETIC SURVEY 1978 RECOVERED IN GOOD CONDITION.

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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