U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 7
Station ID: 9416841 PUBLICATION DATE: 12/21/2020
Name: ARENA COVE, PACIFIC OCEAN
CA
NOAA Chart: 18640 Latitude: 38° 54.9' N ( 38.91456)
USGS Quad: POINT ARENA Longitude: 123° 42.7' W (-123.71108)
To reach the tidal bench marks from Highway 1, turn west on Iversen Ave. and
continue 1.8 km (1.1 mi) to the waterfront. The bench marks are located along
Port Road and Point Arena Creek in the vicinity. The tide house is located at
the end of the Arena Cove Pier.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 6841 H 1979
DESIGNATION: 941 6841 H TIDAL
MONUMENTATION: Tidal Station disk VM#: 1011
AGENCY: National Ocean Survey (NOS) IDB PID#: JT9388
SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID:
LATITUDE: 38° 54.7' N ( 38.91211) LONGITUDE: 123° 42.3' W (-123.70453)
The primary bench mark is a disk set in the center of a niche located at the
bottom of a hill, 0.53 km (0.33 mi) east of the inshore end of the Arena Cove
Pier, 92.05 m (302.0 ft) east of a 3 m (10 ft) metal water line cover, 66.75 m
(219.0 ft) west of a 3 m (10 ft) metal water line cover, 18.29 m (60.0 ft) SE of
the most easterly of four large Eucalyptus trees, 9.14 m (30.0 ft) north of the
centerline of Port Road, and 0.46 m (1.5 ft) north of a 0.10 m x 0.10 m x 1.22 m
(0.3 ft x 0.3 ft x 4.0 ft) high white redwood witness post. The bench mark is
set 6 cm (0.2 ft) below grade, crimped to the top of a copper-clad steel rod
driven 2.4 m (7.9 ft) to refusal, and encased in a 4-inch PVC pipe.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 7
Station ID: 9416841 PUBLICATION DATE: 12/21/2020
Name: ARENA COVE, PACIFIC OCEAN
CA
NOAA Chart: 18640 Latitude: 38° 54.9' N ( 38.91456)
USGS Quad: POINT ARENA Longitude: 123° 42.7' W (-123.71108)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 6 1945
DESIGNATION: 941 6841 TIDAL 6
MONUMENTATION: Tidal Station disk VM#: 1005
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: JT9392
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 38° 54.8' N ( 38.91358) LONGITUDE: 123° 42.6' W (-123.71017)
The bench mark is a disk set in the top of a long narrow rock outcropping
located 152.40 m (500.0 ft) south of Arena Cove Pier along the shoreline, 76.20
m (250.0 ft) south of a small stream emptying into the ocean, and 8.84 m (29.0
ft) west of the base of a high cliff.
BENCH MARK STAMPING: 5 1945
DESIGNATION: 941 6841 TIDAL 5
MONUMENTATION: Tidal Station disk VM#: 1006
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: JT9391
SETTING CLASSIFICATION: Retaining wall OPUS PID:
LATITUDE: 38° 54.9' N ( 38.91489) LONGITUDE: 123° 42.6' W (-123.70981)
The bench mark is a disk set in the top of a retaining wall located east of the
boat house at Arena Cove Ocean Fresh Building, just west of the curve in the
retaining wall, 7.92m (25.98 ft) West of West end of green propane tank, 3.05 m
(10.0 ft) east from the east face of the boat house, and 0.55 m (1.8 ft) north
of the south edge of the wall.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 7
Station ID: 9416841 PUBLICATION DATE: 12/21/2020
Name: ARENA COVE, PACIFIC OCEAN
CA
NOAA Chart: 18640 Latitude: 38° 54.9' N ( 38.91456)
USGS Quad: POINT ARENA Longitude: 123° 42.7' W (-123.71108)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 6841 D 1977
DESIGNATION: 941 6841 D TIDAL
MONUMENTATION: Tidal Station disk VM#: 1007
AGENCY: National Ocean Survey (NOS) IDB PID#: JT9390
SETTING CLASSIFICATION: Concrete step OPUS PID:
LATITUDE: 38° 54.8' N ( 38.91406) LONGITUDE: 123° 42.5' W (-123.70778)
The bench mark is a disk set in the second lowest concrete step located in the
stairway leading to the former Coast Guard Quarters, 0.24 km (0.15 mi) east of
the inshore end of the Arena Cove Pier, 30.48 m (100.0 ft) NNE of the centerline
of Port Street which leads to the Arena Cove Pier, 1.83 m (6.0 ft) west of the
west corner of a double doored wooden Arena Cove Lift Boat station, and 0.12 m
(0.4 ft) west of the eastern corner of the second step.
BENCH MARK STAMPING: 6841 J 1979
DESIGNATION: 941 6841 J TIDAL
MONUMENTATION: Tidal Station disk VM#: 1012
AGENCY: National Ocean Survey (NOS) IDB PID#: JT9387
SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID#: JT9387
LATITUDE: 38° 54.6' N ( 38.91069) LONGITUDE: 123° 42.1' W (-123.70194)
The bench mark is a disk set in a planter triangle located in between a split
driveway and Port Road at 240 Port Road, about 0.8 km (0.5 mi) east of the
inshore end of the Arena Cove pier, 11.81 m (38.8 ft) SW of a wood fence corner,
10.06 m (33.0 ft) north of the centerline of Port Road, 4.95 m (16.2 ft) south
of the split in the driveway, and 1.00 m (3.3 ft) west of a 0.10 m x 0.10 m x
1.22 m (0.3 ft x 0.3 ft x 4.0 ft) high white painted redwood witness post. The
bench mark is set 46 cm (1.5 ft) below grade, crimped to the top of a
copper-clad steel rod driven 1.19 m (3.9 ft) to refusal, and encased in a 4-inch
PVC pipe.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 7
Station ID: 9416841 PUBLICATION DATE: 12/21/2020
Name: ARENA COVE, PACIFIC OCEAN
CA
NOAA Chart: 18640 Latitude: 38° 54.9' N ( 38.91456)
USGS Quad: POINT ARENA Longitude: 123° 42.7' W (-123.71108)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 6841 N 1990
DESIGNATION: 941 6841 N
MONUMENTATION: Tidal Station disk VM#: 1015
AGENCY: National Ocean Service (NOS) IDB PID:
SETTING CLASSIFICATION: Concrete bull rail OPUS PID:
LATITUDE: 38° 54.9' N ( 38.91447) LONGITUDE: 123° 42.7' W (-123.71103)
The bench mark is a disk set in the south concrete bullrail located at the Point
Arena Pier, 16.15 m (53.0 ft) east of the west end of the pier, 2.13 m (7.0 ft)
west of the base of a crane on the south side of the pier, and 0.15 m (0.5 ft)
north of the south face of the pier.
BENCH MARK STAMPING: 6841 S 2007
DESIGNATION: 941 6841 S
MONUMENTATION: Flange-encased Rod VM#: 18485
AGENCY: National Ocean Service (NOS) IDB PID:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID#: BBDY62
LATITUDE: 38° 54.8' N ( 38.91328) LONGITUDE: 123° 42.4' W (-123.70644)
The benchmark is a rod located 92.50 m (303.5 ft) east of PG&E light pole #64,
8.50 m (27.9 ft) south of the centerline of Iverson Ave. (Port Rd.), 3.13 m
(10.3 ft) SSW from an 8" diameter wooden post with reflectors, 0.50 m (1.6 ft)
west from the east end of a stone wall, and 0.32 m (1.0 ft) north of the stone
wall. The datum point of the mark is 10 cm (0.3 ft) below ground level, being
the top of a 9/16" steel rod driven 9.8 m (32.0 ft) to refusal, encased in a 6"
pvc pipe set in concrete with an aluminum access cover.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 7
Station ID: 9416841 PUBLICATION DATE: 12/21/2020
Name: ARENA COVE, PACIFIC OCEAN
CA
NOAA Chart: 18640 Latitude: 38° 54.9' N ( 38.91456)
USGS Quad: POINT ARENA Longitude: 123° 42.7' W (-123.71108)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 6841 U 2016
DESIGNATION: 941 6841 U
MONUMENTATION: Tidal Station disk VM#: 22155
AGENCY: National Ocean Service (NOS) IDB PID:
SETTING CLASSIFICATION: OPUS PID:
LATITUDE: 38° 54.8' N ( 38.91386) LONGITUDE: 123° 42.4' W (-123.70736)
The bench mark is a disk located 16.30 m (53.5 ft) SW of a red fire hydrant,
8.60 m (28.2 ft) south of the centerline of Iverson Ave. (Port Rd.), 8.10 m
(26.6 ft) SE of PG&E light pole number 64. The datum point of the mark is 1 m
(3.3 ft) above ground level, located on top of a stone pillar of a stone wall.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 7
Station ID: 9416841 PUBLICATION DATE: 12/21/2020
Name: ARENA COVE, PACIFIC OCEAN
CA
NOAA Chart: 18640 Latitude: 38° 54.9' N ( 38.91456)
USGS Quad: POINT ARENA Longitude: 123° 42.7' W (-123.71108)
T I D A L D A T U M S
Tidal datums at ARENA COVE, PACIFIC OCEAN based on:
LENGTH OF SERIES: 27 YEARS
TIME PERIOD: 05/1991 - 04/2008, 05/2009 - 04/2019
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9415020 POINT REYES, DRAKES BAY
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (02/06/1998) = 2.643
MEAN HIGHER HIGH WATER MHHW = 1.789
MEAN HIGH WATER MHW = 1.584
MEAN TIDE LEVEL MTL = 0.968
MEAN SEA LEVEL MSL = 0.957
MEAN LOW WATER MLW = 0.352
North American Vertical Datum NAVD88 = 0.042
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (05/18/2003) = -0.801
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
6841 H 1979 7.725 6.141
6 1945 2.786 1.202
5 1945 6.241 4.657
6841 D 1977 7.457 5.873
6841 J 1979 13.962 12.378
6841 N 1990 8.704 7.120
6841 S 2007 6.446 4.862
6841 U 2016 6.978 5.394
Foot Notes:
Bench mark 6841 U 2016 is based on one differential leveling connection and does
not meet the quality control standards of the NOS. Therefore, caution should be
used when deriving elevations for this mark.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 7
Station ID: 9416841 PUBLICATION DATE: 12/21/2020
Name: ARENA COVE, PACIFIC OCEAN
CA
NOAA Chart: 18640 Latitude: 38° 54.9' N ( 38.91456)
USGS Quad: POINT ARENA Longitude: 123° 42.7' W (-123.71108)
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.