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Datums Page Page 1 of 9
Station ID: 9415020 PUBLICATION DATE: 04/21/2003
Name: POINT REYES, DRAKES BAY
CA
NOAA Chart: 18647 Latitude: 37° 59.8' N ( 37.99670)
USGS Quad: DRAKES BAY Longitude: 122° 58.5' W (-122.97500)
To reach the tidal bench marks from Inverness Post Office, proceed 23.5 km (14.6
mi) NW along Sir Francis Drake Highway (taking the right fork to Point Reyes
Beach south), turn left onto Chimney Rock Road (an unmarked road immediately
after passing a dairy farm), follow macadam road and turn left at the parking
lot Y intersection, and follow the road down to a private pier. The bench marks
are located along the road leading to the pier. The tide gauge is located 3 m
(11 ft) east of the south corner of the pier.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: BM B243 1949
DESIGNATION: B 243
MONUMENTATION: Survey disk VM#: 1732
AGENCY: California State Lands Commision IDB PID#: HT1839
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 37° 59.7' N ( 37.99578) LONGITUDE: 122° 58.6' W (-122.97733)
The primary bench mark is a disk set in bedrock on NE slope of an outcrop at the
first rocky point SE of Point St. Joseph Fish Company Pier, about 0.3 km (0.2
mi) NW along the beach from the former U.S. Coast Guard pier, 13.72 m (45.0 ft)
SE of the extended centerline of Point St. Joseph Fish Company Pier, and 1.22 m
(4.0 ft) above ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 9
Station ID: 9415020 PUBLICATION DATE: 04/21/2003
Name: POINT REYES, DRAKES BAY
CA
NOAA Chart: 18647 Latitude: 37° 59.8' N ( 37.99670)
USGS Quad: DRAKES BAY Longitude: 122° 58.5' W (-122.97500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: BM A243 1949
DESIGNATION: A 243
MONUMENTATION: Survey disk VM#: 1731
AGENCY: California State Lands Commision IDB PID#: HT1838
SETTING CLASSIFICATION: Concrete post OPUS PID:
LATITUDE: 37° 59.8' N ( 37.99606) LONGITUDE: 122° 58.7' W (-122.97756)
The bench mark is a disk set in top of a concrete post about 300 m (984 ft) NW
along beach from former Coast Guard pier, 50 m (163 ft) east of the center of a
1 m (2 ft) square concrete post, 37.19 m (122.0 ft) NW of bench mark B243 1949,
6.04 m (19.8 ft) NW of a utility pole, 0.64 m (2.1 ft) south of an orange
witness post, and 0.09 m (0.3 ft) below ground level.
BENCH MARK STAMPING: 5020 J 1978
DESIGNATION: 941 5020 J TIDAL
MONUMENTATION: Tidal Station disk VM#: 1738
AGENCY: National Ocean Survey (NOS) IDB PID#: HT3510
SETTING CLASSIFICATION: Galvanized steel rod OPUS PID:
LATITUDE: 37° 59.7' N ( 37.99478) LONGITUDE: 122° 58.6' W (-122.97600)
The bench mark is a disk located 28 m (92 ft) east of the intersection of
Macadam and dirt road, 16.76 m (55.0 ft) west of an utility pole, 4.11 m (13.5
ft) NNE of the centerline of Macadam road, and 0.91 m (3.0 ft) NNE of a 4x4-inch
redwood witness post. The bench mark is set flush with the ground level,
crimped to a galvanized steel rod driven 4.9 m (16 ft) to refusal, and encased
in a 4-inch plastic pipe.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 9
Station ID: 9415020 PUBLICATION DATE: 04/21/2003
Name: POINT REYES, DRAKES BAY
CA
NOAA Chart: 18647 Latitude: 37° 59.8' N ( 37.99670)
USGS Quad: DRAKES BAY Longitude: 122° 58.5' W (-122.97500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5020 K 1978
DESIGNATION: 941 5020 K TIDAL
MONUMENTATION: Tidal Station disk VM#: 1739
AGENCY: National Ocean Survey (NOS) IDB PID#: HT3504
SETTING CLASSIFICATION: Galvanized steel rod OPUS PID#: HT3504
LATITUDE: 37° 59.8' N ( 37.99628) LONGITUDE: 122° 58.8' W (-122.97944)
The bench mark is a disk located 198 m (650 ft) west along Macadam road from
bench mark BM A243 1949, 91 m (300 ft) north of the intersection of Macadam road
and the road leading west to Sir Francis Drake Highway, 4.88 m (16.0 ft) SE of
the centerline of Macadam road leading to Point St. Joseph Fish Pier, and 0.61 m
(2.0 ft) SE of a 4x4-inch redwood witness post. The bench mark is set 6 cm (0.2
ft) below ground level, crimped to the top of a galvanized steel rod driven 6.1
m (20 ft) to refusal, and encased in a 4-inch PVC pipe.
BENCH MARK STAMPING: 5020 L 1983
DESIGNATION: 941 5020 L TIDAL
MONUMENTATION: Tidal Station disk VM#: 1740
AGENCY: National Ocean Service (NOS) IDB PID#: HT3506
SETTING CLASSIFICATION: Concrete post OPUS PID:
LATITUDE: 37° 59.8' N ( 37.99611) LONGITUDE: 122° 58.7' W (-122.97811)
The bench mark is a disk set in the top center of a 0.55 m (1.8 ft) diameter
cylindrical concrete post that was formerly used as an inshore pier piling at
the toe of a bedrock outcropping, 66 m (218 ft) NW of the inshore end of Point
St. Joseph Fish Company Pier, 55.63 m (182.5 ft) NW of a utility pole, 50.23 m
(164.8 ft) NW of bench mark BM A243 1949, 13.87 m (45.5 ft) north of the center
of Macadam Road, 1.58 m (5.2 ft) NW of an orange witness post, and 0.61 m (2.0
ft) above ground level on seaward side.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 9
Station ID: 9415020 PUBLICATION DATE: 04/21/2003
Name: POINT REYES, DRAKES BAY
CA
NOAA Chart: 18647 Latitude: 37° 59.8' N ( 37.99670)
USGS Quad: DRAKES BAY Longitude: 122° 58.5' W (-122.97500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5020 M 1985
DESIGNATION: 941 5020 M TIDAL
MONUMENTATION: Tidal Station disk VM#: 1741
AGENCY: National Ocean Service (NOS) IDB PID#: HT3503
SETTING CLASSIFICATION: Stainless steel rod OPUS PID#: HT3503
LATITUDE: 37° 59.7' N ( 37.99575) LONGITUDE: 122° 58.8' W (-122.97917)
The bench mark is a disk located 69 m (225 ft) SE of bench mark 5020 K 1978, 41
m (135 ft) west of power pole # B2, 21.24 m (69.7 ft) east of a metal brown and
white roadside sign "docks are closed to public use", 8.47 m (27.8 ft) west from
the east end of a wooden guard rail at the fork of Chimney Rock Road, 7.96 m
(26.1 ft) east from the west end of the wooden guard rail, 1.37 m (4.5 ft)
seaward of wooden guard rail and a guard rail post that has a metal witness sign
attached. The bench mark is set 15 cm (0.6 ft) below ground level, beneath an
aluminum access cover, crimped to the top of a stainless steel rod driven 4.3 m
(14 ft) to refusal, and protected by a concrete sleeve.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 9
Station ID: 9415020 PUBLICATION DATE: 04/21/2003
Name: POINT REYES, DRAKES BAY
CA
NOAA Chart: 18647 Latitude: 37° 59.8' N ( 37.99670)
USGS Quad: DRAKES BAY Longitude: 122° 58.5' W (-122.97500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5020 N 1985
DESIGNATION: 941 5020 N TIDAL
MONUMENTATION: Tidal Station disk VM#: 1742
AGENCY: National Ocean Service (NOS) IDB PID#: HT3507
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 37° 59.7' N ( 37.99492) LONGITUDE: 122° 58.6' W (-122.97661)
The bench mark is a disk located 15.27 m (50.1 ft) WNW of the NW corner of the
concrete steps leading to the front of a two-story residence on the road leading
to the Coast Guard boat house, 14.45 m (47.4 ft) NW of a red water pipe
protruding vertically 0.76 m (2.5 ft) above the west lawn of the residence,
12.62 m (41.4 ft) south of the nearest power pole, 5.43 m (17.8 ft) SSE of a
1.37 m (4.5 ft) high white wooden post, 1.92 m (6.3 ft) WNW of the nearest tree,
and 0.46 m (1.5 ft) south of a white witness post. The bench mark is set 15 cm
(0.5 ft) below ground level, beneath an aluminum access cover, crimped to the
top of a stainless steel rod driven 4.6 m (15 ft) to refusal, and protected by
a concrete sleeve.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 9
Station ID: 9415020 PUBLICATION DATE: 04/21/2003
Name: POINT REYES, DRAKES BAY
CA
NOAA Chart: 18647 Latitude: 37° 59.8' N ( 37.99670)
USGS Quad: DRAKES BAY Longitude: 122° 58.5' W (-122.97500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5020 P 1985
DESIGNATION: 941 5020 P TIDAL
MONUMENTATION: Tidal Station disk VM#: 1743
AGENCY: National Ocean Service (NOS) IDB PID#: HT3508
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 37° 59.7' N ( 37.99472) LONGITUDE: 122° 58.6' W (-122.97722)
The bench mark is a disk located on a hillside about 137 m (450 ft) SE of bench
mark 5020 N 1985, 37 m (120 ft) SE of bench mark 5020 R 1985, 18 m (58 ft) east
of a barbed wire fence, 10 m (32 ft) SE of the southern-most of two 1 m (4 ft)
high brown fiberglass roadside reflectors marking a drainage pipe crossing
beneath the roadway, 7.62 m (25.0 ft) south of the centerline of the road that
leads to the Coast Guard boat house, and 0.30 m (1 ft) north of an orange NOS
fiberglass witness post. The bench mark is set 15 cm (0.5 ft) below ground,
beneath an aluminum access cover, crimped to the top of a stainless steel rod
driven 4.6 m (15 ft) to absolute refusal, and protected by a concrete sleeve.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 9
Station ID: 9415020 PUBLICATION DATE: 04/21/2003
Name: POINT REYES, DRAKES BAY
CA
NOAA Chart: 18647 Latitude: 37° 59.8' N ( 37.99670)
USGS Quad: DRAKES BAY Longitude: 122° 58.5' W (-122.97500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5020 Q 1985
DESIGNATION: 941 5020 Q TIDAL
MONUMENTATION: Tidal Station disk VM#: 1744
AGENCY: National Ocean Service (NOS) IDB PID#: HT3505
SETTING CLASSIFICATION: Stainless steel rod OPUS PID#: HT3505
LATITUDE: 37° 59.8' N ( 37.99639) LONGITUDE: 122° 58.7' W (-122.97903)
The bench mark is a disk located 58 m (191 ft) north of bench mark 5020 M 1985,
46 m (151 ft) east of bench mark 5020 K 1978, 4.57 m (15.0 ft) north of the
centerline of the road leading to Point St. Joseph Fish Company Pier, and 2.44 m
(8.0 ft) west of an orange NOS fiberglass witness post. The bench mark is set
15 cm (0.5 ft) below the ground, beneath an aluminum access cover, crimped to
the top of a stainless steel rod driven 2.4 m (8 ft) to absolute refusal, and
protected by a concrete sleeve.
BENCH MARK STAMPING: 5020 R 1985
DESIGNATION: 941 5020 R TIDAL
MONUMENTATION: Tidal Station disk VM#: 1745
AGENCY: National Ocean Service (NOS) IDB PID#: HT3509
SETTING CLASSIFICATION: Concrete retaining wall OPUS PID:
LATITUDE: 37° 59.7' N ( 37.99503) LONGITUDE: 122° 58.6' W (-122.97736)
The bench mark is a disk set in a concrete retaining wall which runs along the
SW side of a driveway that leads to a garage, 73 m (240 ft) SE of bench mark
5020 N 1985, 37 m (120 ft) NW of bench mark 5020 P 1985, 0.49 m (1.6 ft) west of
the most western corner of garage, 0.49 m (1.6 ft) west of a water faucet, and
0.09 m (0.3 ft) above the driveway level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 8 of 9
Station ID: 9415020 PUBLICATION DATE: 04/21/2003
Name: POINT REYES, DRAKES BAY
CA
NOAA Chart: 18647 Latitude: 37° 59.8' N ( 37.99670)
USGS Quad: DRAKES BAY Longitude: 122° 58.5' W (-122.97500)
T I D A L D A T U M S
Tidal datums at POINT REYES, DRAKES BAY based on:
LENGTH OF SERIES: 19 Years
TIME PERIOD: January 1983 - December 2001
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION:
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (02/06/1998) = 2.604
MEAN HIGHER HIGH WATER MHHW = 1.758
MEAN HIGH WATER MHW = 1.554
MEAN TIDE LEVEL MTL = 0.958
MEAN SEA LEVEL MSL = 0.946
MEAN LOW WATER MLW = 0.361
North American Vertical Datum NAVD88 = 0.008
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (01/19/1988) = -0.819
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
BM B243 1949 3.771 2.217
BM A243 1949 3.532 1.978
5020 J 1978 25.242 23.688
5020 K 1978 24.343 22.789
5020 L 1983 5.956 4.402
5020 M 1985 32.468 30.914
5020 N 1985 27.684 26.130
5020 P 1985 19.862 18.308
5020 Q 1985 19.820 18.267
5020 R 1985 21.594 20.040
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 9 of 9
Station ID: 9415020 PUBLICATION DATE: 04/21/2003
Name: POINT REYES, DRAKES BAY
CA
NOAA Chart: 18647 Latitude: 37° 59.8' N ( 37.99670)
USGS Quad: DRAKES BAY Longitude: 122° 58.5' W (-122.97500)
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 NGS's Integrated Data Base (IDB PID)
provides geodetic datum based on traditionally leveled and bluebooked ties to
the National Spatial Reference System(NSRS) https://www.ngs.noaa.gov/datasheets/.
The NGS Online Positioning User Service (OPUS PID) provides geodetic datum based
on GPS position & tie it to the NSRS https://www.ngs.noaa.gov/OPUS/.
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.