Berntsen Monument Marks the Mile
A Mile High Benchmark, based on NAVD88 datum, was set in the face of the 13th step of the Colorado State Capitol on September 29, 2003. Colorado Governor Bill Owens presided over the benchmark setting ceremony on the west steps of the capitol on a crisp, sunny Colorado morning.
The new Benchmark, featuring the Rocky Mountains as depicted on the Colorado State Seal, joins two existing monuments. A plaque adhered to the fifteenth step in 1909 established the first Mile High marker. After several plaques were stolen, the words “One Mile Above Sea Level” were carved into the native Colorado granite in 1947. Three steps higher is a brass cap set in 1969 by Colorado State University engineering students using NGVD29 datum. The difference between NGVD29 datum and NAVD88 datum at this location is 0.92 meters or 3.03 feet.
The NAVD88 brass cap is a standard Berntsen concrete marker and was the second Berntsen monument set for this project. Previously, as the first phase of the project, HWS-001, a Top Security rod monument set in a benchmark access cover was driven to refusal at the foot of the west steps of the capitol.
Phase two involved running differential levels between HARN station McDonnell on the campus of The Metropolitan State College in Denver, two NGS monuments at Union Station Railroad station, and HWS-001.
While State Capitol employees nervously watched, a hole was drilled into the 13th step to hold the new BM. This was the completion of the 3rd phase of work. A level loop was run from the newly calculated HWS-001 up the steps of the capitol to determine the location of the new Benchmark.
The ceremony to set the NAVD88 Mile High Benchmark was the result of many months of emails, meetings with State officials, phone calls and schedule checking to put together the three Saturdays that were needed to accomplish our mission. The Professional Land Surveyors of Colorado (PLSC) whose members comprise federal, state, county, city and private surveyors are quite proud and honored to be involved in the setting of the NAVD88 Mile High Benchmark.
Report compiled by Michael M. Greer, PLS. Mike, Land Analyst for Jefferson County Planning & Zoning, was PLSC’s Project Coordinator for the Mile High Benchmark project.
Originally published in the Berntsen SurveyLog Volume 15, Number 1 (January, 2004)