Our Summit Markers are artistic representations of the markers
one would typically find on the summit of a mountain and at
various other locations across the United States and other
countries of the world. The information depicted on these
tablets is derived from the best information available from
the US Geological Survey and/or the National Geodetic Survey.
The data on the markers is informational only and should not
be used for survey control or navigation.
In 1929, the National Geodetic Survey (NGS) compiled all
of the existing vertical benchmarks and created the National
Geodetic Vertical Datum of 1929 (NGVD 29). Since then, movements
of the Earth's crust have changed the elevations of many benchmarks.
In 1988, NGVD 29 was adjusted to remove inaccuracies and to
correct distortions. The new datum, called the North American
Vertical Datum of 1988 (NAVD 88), is the most commonly used
vertical datum in the United States today. In the Rocky Mountain
region there may be increases in elevation by as much as 7
feet between the old NGVD 29 standard and the new NAVD 88
standard. In Florida, however, the opposite is true –
elevations of the newer standard are lower than the older.
In 1927 the U.S. Coast and Geodetic Survey, the predecessor
of the National Geodetic Survey, "connected" all
of the existing horizontal (Latitude and Longitude) monuments
together and created the North American Datum of 1927 (NAD
27). This datum was used extensively during the next 60 years
as the primary reference for horizontal positioning. In 1983,
NAD 27 was adjusted to remove inaccuracies and to correct
distortions. The new datum, called NAD 83, is the most commonly
used horizontal positioning datum today in the United States.
Our markers, with only a few exceptions noted below, use
the most recent data standards for ascribing elevation (NAVD
88 – North American Vertical Datum) and Latitude and
Longitude (NAD 83 – North American Datum). Credit for
the surveying government body (U.S. Coast and Geodetic Survey
or U.S. Geological survey) was given to the original surveying
body based upon various sources – NGS Datasheets (www.ngs.noaa.gov),
U.S.G.S. datasheets (www.usgs.gov) or provided by resources
within either department. The type of marker (e.g. Bench Mark.)
was derived from the best information available from the resources
cited above. In many cases the markers on the top of mountains
have been destroyed, have never been placed originally, or
are indicated by some other object such as a cairn, or as
in the case of Mount Elbert in Colorado, a simple bolt and
washer drilled and cemented into stone. Where it was not clear
from the data sheet which type of marker it was we defaulted
to Bench Mark. Each type of marker (e.g. Bench Mark, Triangulation
Station, Reference Mark) is used for different purposes or
has varying levels of accuracy so it is important to understand
that our markers are not to be used for survey control. Where
there were no datasheets available we used the elevation on
maps (which largely still employ the NGVD 29 standard) and
converted it using NGS’ VERTCON Software to determine
the elevation in NAVD88 terms.
to view or purchase our Summit Markers
We did not convert to the NAVD 88 vertical datum for the Mount
St. Helens Markers. The two markers show the elevation, latitude
and longitude, and the date just prior to the eruption (May
17, 1980) and just after (May 19, 1980). No surveys were conducted
on those days - they simply represent the before/after scenario
of the highest point. The eruption occurred on May 18, 1980.
The data for Mount St. Helens was derived with the help of
a few folks at the U.S.G.S. site in Denver Colorado.
The elevation on the Death Valley Marker was maintained at
the well known minus 282 ft. below sea level.
We at High Mountains Merchandise are grateful for the help
that the staff at the National Geodetic Survey and U.S. Geological
Survey have provided over a several month period. They were
more than patient in providing lessons in Geodesy and answering
the many questions presented to them regarding the research
of our products.
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