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.
******Due to this you may see different altitudes on our markers vs older ratings. Please be aware that we use the most recent data.******
Click here 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.Com 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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