U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
Datums Page                                                        Page  1 of  7

                                                                                
Station ID: 9451349                         PUBLICATION DATE:  09/17/2008
Name:       THE SUMMIT, N.W. SUMMIT ISLAND                    
            AK
NOAA Chart: 17372                           Latitude:   56° 40.9' N (  56.68170)
USGS Quad:  PETERSBURG (C-9)                Longitude: 133° 44.1' W (-133.73500)


To reach the bench marks from Point Baker on the north tip of Prince of Wales
Island via boat, proceed approximately northerly 32.8 km (17.7 nm) crossing
Sumner Strait through Keku Straits to Devils Elbow, then proceed cautiously
through Devils Elbow westerly and then northerly for 6.6 km (3.6 nm) to the area
known as The Summit at the south end of Rocky Pass.  The bench marks are on a
group of three islands just west of the green daymark "27" at The Summit.  The
daymark is on the east tip of the northeasterly most of the three islands, on
the west side of the dredged channel.  The three islands are connected at about
half tide.  The tide gauges were established at the southwest corner of the
southerly of the three islands (at the location of tidal bench mark 1 1929). 
Use extreme caution due to high currents and many rocks in this area.


                         T I D A L   B E N C H   M A R K S


                 PRIMARY BENCH MARK STAMPING:  1 1929
                         DESIGNATION:          945 1349 TIDAL 1

MONUMENTATION:           Tidal Station disk                    VM#:        18116
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:        
SETTING CLASSIFICATION:  Rock                                  OPUS PID#: BBBG28
LATITUDE:   56° 40.9' N (  56.68219)          LONGITUDE: 133° 44.1' W (-133.73531)


The primary bench mark is a disk set flush in the top of a rock about 2 m (7 ft)
square and is on the SW corner of the south island, 190 m (623 ft) from the
north point of the island that is west of the area across the channel and
bearing 285 T (260 M), 59.0 m (193.6 ft) south of bench mark 945 1349 TIDAL 3,
38.35 m (125.8 ft) SW from bench mark 945 1349 TIDAL 2, approximately 5 m (16
ft) west of the tree line, and approximately 1.0 m (3.3 ft) above the apparent
mean high water line.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  2 of  7

                                                                                
Station ID: 9451349                         PUBLICATION DATE:  09/17/2008
Name:       THE SUMMIT, N.W. SUMMIT ISLAND                    
            AK
NOAA Chart: 17372                           Latitude:   56° 40.9' N (  56.68170)
USGS Quad:  PETERSBURG (C-9)                Longitude: 133° 44.1' W (-133.73500)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  2 1929
                         DESIGNATION:          945 1349 TIDAL 2

MONUMENTATION:           Tidal Station disk                    VM#:        18117
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:        
SETTING CLASSIFICATION:  Rock                                  OPUS PID:        
LATITUDE:   56° 40.9' N (  56.68169)          LONGITUDE: 133° 44.2' W (-133.73622)


The bench mark is a disk set in the top of a rock about 2 m (7 ft) square, on
the north side of the south island in a group that is about 230 m (755 ft) west
of part of Keku Strait called The Summit, 50 m (164 ft) from bench mark 945 1349
TIDAL 4, 43.24 m (141.9 ft) SE of bench mark 945 1349 TIDAL 4, 38.35 m (125.8
ft) NE from bench mark 945 1349 TIDAL 1, 33.16 m (108.8 ft) SW from bench mark
945 1349 TIDAL 5, and approximately 1.5 m (4.9 ft) above the apparent mean high
water line.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  3 of  7

                                                                                
Station ID: 9451349                         PUBLICATION DATE:  09/17/2008
Name:       THE SUMMIT, N.W. SUMMIT ISLAND                    
            AK
NOAA Chart: 17372                           Latitude:   56° 40.9' N (  56.68170)
USGS Quad:  PETERSBURG (C-9)                Longitude: 133° 44.1' W (-133.73500)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  3 1929
                         DESIGNATION:          945 1349 TIDAL 3

MONUMENTATION:           Tidal Station disk                    VM#:        18118
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:        
SETTING CLASSIFICATION:  Rock                                  OPUS PID:        
LATITUDE:   56° 40.9' N (  56.68242)          LONGITUDE: 133° 44.2' W (-133.73711)


The bench mark is a disk set in the top of a large rock about 3 m (9 ft) square
on the SW corner of the Northwest Island of a group that is about 230 m (755 ft)
west of part of Keku Strait called The Summit the area consisting of a group of
three islands (Northwest, East, and South) which are connected by a ledge at low
water with Green daymark "27" set on the eastern ledge of the easternmost
island, 59 m (194 ft) north of bench mark 945 1349 TIDAL 1, 17.24 m (56.7 ft)
west of bench mark 945 1349 TIDAL 4, approximately 3 m (10 ft) SW from the tree
line, approximately 2 m (6 ft) NE of mean high water line, and approximately
0.25 m (0.8 ft) above the apparent mean high water line.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  4 of  7

                                                                                
Station ID: 9451349                         PUBLICATION DATE:  09/17/2008
Name:       THE SUMMIT, N.W. SUMMIT ISLAND                    
            AK
NOAA Chart: 17372                           Latitude:   56° 40.9' N (  56.68170)
USGS Quad:  PETERSBURG (C-9)                Longitude: 133° 44.1' W (-133.73500)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  1349 4 2006
                         DESIGNATION:          945 1349 TIDAL 4

MONUMENTATION:           Tidal Station disk                    VM#:        18119
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Rock                                  OPUS PID:        
LATITUDE:   56° 40.9' N (  56.68228)          LONGITUDE: 133° 44.2' W (-133.73656)


The bench mark is a disk set flush on a 1 m x 0.5 m (3.3 ft x 1.6 ft) rock on
the SE corner of the NW island in a group that is about 200 m (656 ft) west of
part of Keku Strait called The Summit the area consisting of a group of three
islands (Northwest, East, and South) that are connected by a ledge at low water
with Green daymark "27" set on the eastern ledge of the easternmost island,
58.12 m (190.7 ft) west of bench mark 945 1349 TIDAL 5, 43.24 m (141.9 ft) NW of
bench mark 945 1349 TIDAL 2, 40 m (131.2 ft) from the tallest tree on the South
Island bearing 160 T (135 M), 17.24 m (56.7 ft) east of bench mark 945 1349
TIDAL 3, 10 m (33 ft) NE of mean high water line, 2 m (6 ft) south of the tree
line, and approximately 1.1 m (3.6 ft) above the apparent mean high water line.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  5 of  7

                                                                                
Station ID: 9451349                         PUBLICATION DATE:  09/17/2008
Name:       THE SUMMIT, N.W. SUMMIT ISLAND                    
            AK
NOAA Chart: 17372                           Latitude:   56° 40.9' N (  56.68170)
USGS Quad:  PETERSBURG (C-9)                Longitude: 133° 44.1' W (-133.73500)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  1349 5 2006
                         DESIGNATION:          945 1349 TIDAL 5

MONUMENTATION:           Tidal Station disk                    VM#:        18120
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Rock                                  OPUS PID:        
LATITUDE:   56° 40.9' N (  56.68211)          LONGITUDE: 133° 44.1' W (-133.73572)


The bench mark is a disk set flush in a 3 m x 2 m (10 ft x 7 ft) rock on the SE
corner of the east island in a group that is about 200 m (656 ft) west of part
of Keku Strait called The Summit, the area consisting of a group of three
islands (Northwest, East, and South) that are connected by a ledge at low water
with Green daymark "27" set on the eastern ledge of the easternmost island,
58.12 m (190.7 ft) east of bench mark 945 1349 TIDAL 4, 45 m (148 ft) 235 T (210
M) of the tallest tree on the South Island, 33.16 m (108.8 ft) NE from bench
mark 945 1349 TIDAL 5, 6.49 m (21.3 ft) north of the mean high water line, 5 m
(16 ft) south of the treeline, and approximately 0.6 m (2 ft) above the apparent
mean high water line.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  6 of  7

                                                                                
Station ID: 9451349                         PUBLICATION DATE:  09/17/2008
Name:       THE SUMMIT, N.W. SUMMIT ISLAND                    
            AK
NOAA Chart: 17372                           Latitude:   56° 40.9' N (  56.68170)
USGS Quad:  PETERSBURG (C-9)                Longitude: 133° 44.1' W (-133.73500)


                            T I D A L   D A T U M S 


Tidal datums at THE SUMMIT, N.W. SUMMIT ISLAND based on:

     LENGTH OF SERIES:      1 MONTH
     TIME PERIOD:           August 2007 - August 2007
     TIDAL EPOCH:           1983-2001
     CONTROL TIDE STATION:  9450460 KETCHIKAN, TONGASS NARROWS


Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:

     MEAN HIGHER HIGH WATER                     MHHW   =  4.631
     MEAN HIGH WATER                            MHW    =  4.365
     MEAN SEA LEVEL                             MSL    =  2.449
     MEAN TIDE LEVEL                            MTL    =  2.429
     MEAN LOW WATER                             MLW    =  0.492
     MEAN LOWER LOW WATER                       MLLW   =  0.000

North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In METERS above:

     Stamping or Designation                    MLLW        MHW

     1 1929                                      5.522    1.157
     2 1929                                      5.948    1.583
     3 1929                                      4.741    0.376
     1349 4 2006                                 5.573    1.208
     1349 5 2006                                 5.064    0.699


                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  7 of  7

                                                                                
Station ID: 9451349                         PUBLICATION DATE:  09/17/2008
Name:       THE SUMMIT, N.W. SUMMIT ISLAND                    
            AK
NOAA Chart: 17372                           Latitude:   56° 40.9' N (  56.68170)
USGS Quad:  PETERSBURG (C-9)                Longitude: 133° 44.1' W (-133.73500)


                             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.