U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
PUBLICATION DATE: 10/07/1982
Station ID: 9414906 SUPERCEDED DATE: 04/21/2003
Name: POINT BONITA, BONITA COVE,GOLDEN GATE
CALIFORNIA
NOAA Chart: 18649 Latitude: 37° 49.1' N
USGS Quad: POINTBONITA Longitude: 122° 31.7' W
To reach the tidal bench marks proceed north on U.S. Highway 101 across the
Golden Gate Bridge, first exit west to Binker Road and through tunnel, west 3.0
miles (0.00 km) bearing left at fork and then following signs for coast guard
Point Bonita light station. The tide gage and staff were on outer edge of pier
near base of steep cliff underneath light station.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 4906 A 1979
MONUMENTATION: Survey Disk VM#: 8491
AGENCY: PID:
SETTING CLASSIFICATION: Bedrock
The bench mark is set flush on the uppermost point of a ridge of bedrock NE from
easternmost portion of ruins of Coast Guard concrete boathouse, 20.5 feet (6.2
m) NE from concrete wall, and 2 feet (0.6 m) from eastern edge of the ridge of
bedrock.
BENCH MARK STAMPING: 4906 B 1979
MONUMENTATION: Survey Disk VM#: 8492
AGENCY: PID:
SETTING CLASSIFICATION: Bedrock
The bench mark is set flush along top of ridge of gray bedrock, 84 feet (25.6 m)
north of high red boulder, 34 feet (10.4 m) SE of sheer bluff surrounding Bonita
Cove, and 7.5 feet (2.3 m) west of narrow channel between two ridges of bedrock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
PUBLICATION DATE: 10/07/1982
Station ID: 9414906 SUPERCEDED DATE: 04/21/2003
Name: POINT BONITA, BONITA COVE,GOLDEN GATE
CALIFORNIA
NOAA Chart: 18649 Latitude: 37° 49.1' N
USGS Quad: POINTBONITA Longitude: 122° 31.7' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4906 C 1979
MONUMENTATION: Survey Disk VM#: 8493
AGENCY: PID:
SETTING CLASSIFICATION: Bedrock Ledge
The bench mark is set flush in a bedrock ledge directly in line with centerline
of section of abandoned pier offshore, 61 feet (18.6 m) SW from junction of
three railway tracks, and 43 feet (13.1 m) SW from ladder at north end of
abandoned pier.
BENCH MARK STAMPING: 4906 D 1979
MONUMENTATION: Survey Disk VM#: 8494
AGENCY: PID:
SETTING CLASSIFICATION: Bedrock Ledge
The bench mark is set flush in concrete foundation at north corner of U.S. Coast
Guard boathouse ruins, 47 feet (14.3 m) from junction of three railway tracks,
and 35 feet (10.7 m) west of Bench Mark 4906 A 1979.
BENCH MARK STAMPING: 4906 E 1979
MONUMENTATION: Survey Disk VM#: 8495
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Foundation
The bench mark is set flush in bedrock, at base of sheer bluff halfway between
Bench Mark 4906 A 1979 and Bench Mark 4906 B 1979, and 3 feet (0.9 m) west of
large red boulder.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
PUBLICATION DATE: 10/07/1982
Station ID: 9414906 SUPERCEDED DATE: 04/21/2003
Name: POINT BONITA, BONITA COVE,GOLDEN GATE
CALIFORNIA
NOAA Chart: 18649 Latitude: 37° 49.1' N
USGS Quad: POINTBONITA Longitude: 122° 31.7' W
T I D A L D A T U M S
Tidal datums at POINT BONITA, BONITA COVE,GOLDEN GATE based on:
LENGTH OF SERIES: 2 MONTHS
TIME PERIOD: MARCH - APRIL 1979
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 9414290 SAN FRANCISCO
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (02/13/1979) = 7.10
MEAN HIGHER HIGH WATER MHHW = 6.04
MEAN HIGH WATER MHW = 5.49
MEAN TIDE LEVEL MTL = 3.34
MEAN LOW WATER MLW = 1.18
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (04/28/1979) = -1.00
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
4906 A 1979 13.90 8.41
4906 B 1979 14.48 8.99
4906 C 1979 15.80 10.31
4906 D 1979 14.40 8.91
4906 E 1979 17.42 11.93
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
PUBLICATION DATE: 10/07/1982
Station ID: 9414906 SUPERCEDED DATE: 04/21/2003
Name: POINT BONITA, BONITA COVE,GOLDEN GATE
CALIFORNIA
NOAA Chart: 18649 Latitude: 37° 49.1' N
USGS Quad: POINTBONITA Longitude: 122° 31.7' W
D E F I N I T I O N S
Mean Sea Level (MSL) is a tidal datum determined over a 19-year National Tidal
Datum Epoch. It pertains to local mean sea level and should not be confused
with the fixed datums of North American Vertical Datum of 1988 (NAVD88).
NAVD88 is a fixed datum derived from a simultaneous, least squares, minimum
constraint adjustment of Canadian/Mexican/United States leveling observations.
Local mean sea level observed at Father Point/Rimouski, Canada was held fixed as
the single initial constraint. NAVD88 replaces NGVD29 as the national
standard geodetic reference for heights. Bench mark elevations relative to
NAVD88 are available from NGS through the World Wide Web at
National Geodetic Survey.
NGVD29 is a fixed datum adopted as a national standard geodetic reference for
heights but is now considered superseded. NGVD29 is sometimes referred to as
Sea Level Datum of 1929 or as Mean Sea Level on some early issues of Geological
Survey Topographic Quads. NGVD29 was originally derived from a general
adjustment of the first-order leveling networks of the U.S. and Canada after
holding mean sea level observed at 26 long term tide stations as fixed.
Numerous local and wide-spread adjustments have been made since establishment in
1929. Bench mark elevations relative to NGVD29 are available from the National
Geodetic Survey (NGS) data base via the World Wide Web at
National Geodetic Survey.
NAVD88 and NGVD29 are fixed geodetic datums whose elevation relationships to
local MSL and other tidal datums may not be consistent from one location to
another.
The Vertical Mark Number (VM#) and PID# shown on the bench mark sheet are unique
identifiers for bench marks in the tidal and geodetic databases, respectively.
Each bench mark in either database has a single, unique VM# and/or PID# assigned.
Where both VM# and PID# are indicated, both tidal and geodetic elevations are
available for the bench mark listed.
The NAVD88 elevation is shown on the Elevations of Tidal Datums Table Referred
to MLLW only when two or more of the bench marks listed have NAVD88 elevations.
The NAVD88 elevation relationship shown in the table is derived from an average
of several bench mark elevations relative to tide station datum. As a result of
this averaging, NAVD88 bench mark elevations computed indirectly from the tidal
datums elevation table may differ slightly from NAVD88 elevations listed for
each bench mark in the NGS database.