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New Denver Mile-High Bench Mark


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NAVD88 MILE HIGH BENCHMARK CEREMONY

COLORADO STATE CAPITOL, WEST STEPS

SEPTEMBER 29, 2003, 10AM

 

Governor Owens will be dedicating the new Mile High Benchmark.

 

There is already a mile-high bench mark on the capitol. It is at an elevation of about 5280 feet using the National Geodetic Vertical Datum of 1929 (NGVD'29), but is only about 5277 feet using the North American Vertical Datum of 1988 (NAVD'88). The new mark will be at 5280 feet NAVD'88.

 

I guess Denver didn't want the nickname as the "Three Feet Short of a Mile High City"

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Here is something I came across on a Land Surveyors message board:

 

"I had always thought the original 'Mile High Marker' set on the steps of the Colorado State Capitol was done in approximately 1930-1931. Turns out it was much earlier, 1909. That got me to wondering what datum that was on and when the first cross country network was finished. This all led me to an excellent article published in POB which I vaguely remembered. Got lucky and found it. Without POB's permission, here is part of that article.

 

'History of U.S. Geodetic Vertical Datums' by David B. Zilkoski, 10/18/2000

 

'The first leveling route in the United States considered to be of geodetic quality was established in 1856-57 under the direction of G.B. Vose of the U.S. Coast Survey. The leveling survey was required to support current and tide studies in the New York Bay and Hudson River areas. The first leveling line officially designated as "geodesic leveling" by the Coast and Geodetic Survey followed an arc of triangulation along the 39th parallel. This 1887 survey began at bench mark A in Hagerstown, Md.

 

By 1900, the vertical control network had grown to 21,095 km of geodetic leveling. A reference surface was determined in 1900 by holding elevations referenced to local mean sea level (LMSL) fixed at five tide stations. Data from two other tide stations indirectly influenced the determination of the reference surface. Subsequent readjustments of the leveling network were performed by the Coast and Geodetic Survey in 1903, 1907 and 1912.

 

The next general adjustment of the vertical control network was accomplished in 1929. By then, the international nature of geodetic networks was well understood, and Canada provided data for its first-order vertical network to combine with the U.S. network. The two networks were connected at 24 locations through vertical control points (bench marks) from Maine/New Brunswick to Washington/British Columbia. Although Canada did not adopt the "Sea Level Datum of 1929" [name changed to National Geodetic Vertical Datum of 1929 (NGVD 29) in 1973] determined by the United States, Canadian-U.S. cooperation in the general adjustment greatly strengthened the 1929 network."

 

So, I conclude the U.S. was on the 1907 version of the national datum at the time of the setting of that original BM.

 

Bill McComber, PLS CO

 

Bill is a knowledgeable fellow, so I trust his conclusion.

 

Mark

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A new Mile High mark? See my comments on KK1709. Looks like there was a mark before the mark that is now being replaced. And the incription "One Mile Above Sea Level" is on a different riser. Could this be the fourth attempt to establish a mark at 5,280 feet above MSL?

Boy, I hope they don't have to re-paint the seats at Mile High Stadium.

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