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Details for Benchmark: HT1484

N 37° 19.833 W 122° 23.350 (NAD 83)

Altitude: 159.68

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

Location:
In SAN MATEO county, CA View Original Datasheet
Designation:
R 1239
Marker Type:
bench mark disk
Setting:
light structures
Stability:
Mark of questionable or unknown stability.

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N 37° 19.858 W 122° 23.363
Found after visiting a cache in San Gregorio.

Found where described

[Photos:]
photomark
photoeye level
photofor reference
N 37° 19.856 W 122° 23.363

Found in good condition. Description adequate.

[Photos:]
photoHT1484 R 1239
photoHT1484 R 1239 setting

Recovered the Benchmark R 1239, per the 1972 NGS description, in good condition.

[Photos:]
photoR1239

My GPSr: N 37 19.855, W 122 23.364
Easy to find the wall via the datasheet description. Will post a few images. -Batch218-

[Photos:]
photoBenchmark
Benchmark
photoMark with GPSr
Mark with GPSr
photoIn situ
In situ

This one is hard to find because it's on a white headwall and the benchmark has been painted over. Also, oddly enough, it's in the center, not on an end. I've never seen one in the middle before. So since it's camoflagged and not in a "normal" place, it's hard to find.

[Photos:]
photoHT1484.JPG
photoHT1484 Location looking toward San Gregorio.JPG

Documented History (by the NGS)

01/01/1972 by NGS (MONUMENTED)
DESCRIBED BY NATIONAL GEODETIC SURVEY 1972 10.1 MI S FROM HALF MOON BAY. 9.3 MILES SOUTH ALONG STATE HIGHWAY 1 FROM THE JUNCTION OF KELLY AVENUE AT HALF MOON BAY, THENCE 0.8 MILE SOUTH ALONG STAGE ROAD, 0.3 MILE NORTH OF THE JUNCTION OF LA HONDA ROAD AND THE SAN GREGORIO POST OFFICE, IN THE TOP OF THE SOUTHWEST CONCRETE HEAD WALL OF AN 18-INCH PIPE CULVERT, THE HEAD WALL IS 3 1/2-FEET HIGH AND 20-FEET LONG, 7.5 FEET NORTHWEST OF THE SOUTHEAST END OF THE HEAD WALL, 18 1/2 FEET SOUTHWEST OF THE CENTER LINE OF THE ROAD, 44 FEET WEST AND ACROSS THE ROAD FROM A POWER POLE WITH A GUY POLE, AND ABOUT 3 1/2 FEET HIGHER THAN THE ROAD.
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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