FINDING EARLY USGS BENCH MARKS

Finding the early USGS bench marks can be challenging. Most are not indexed in the NGS datasheets for vertical control marks. The descriptions that were published by USGS are often over 100 years old, but with some effort many can still be found.

Two main resources are needed - the quad sheets and the notes. The early quad sheets were mostly 30-minute size with some also done in 15-minute size. Keep in mind that these early bench marks were not used until the 1896 season. Therefore, even though an early quad sheet might have a published date of 1900, the surveying for that quad sheet might have taken place prior to 1896. Check the bottom left corner of the quad sheet for the survey date. If the quad sheet has bench marks, they will almost always be shown on the sheets with an "X" symbol, the letters "B.M." next to it, and an elevation rounded to the nearest foot.

Two websites listed below have most of the early USGS maps. The first is the U. S. Geological Survey's historical map website. The map scale for most of the early quad sheets is 125000.

USGS MAPS

Another good reference is the online Perry-Castaņeda Library Map Collection at the University of Texas. After entering the website below, scroll down to the section that says "Pre-1945 Topographic Maps" and select the desired state.

USGS MAPS
MAP EXAMPLE

Most of the early leveling notes were placed in USGS bulletins. They have been scanned by Google Books and are available online. These bulletins, for example, are titled "Results of Spirit Leveling in Nebraska, 1896-1913 Inclusive". To find a bulletin, click on the link below to go to Google Books. Then type in the appropriate search words for the bulletin such as "Results Spirit Leveling Nebraska" substituting the state for the one you are searching to find.

GOOGLE BOOKS
BULLETIN EXAMPLE


The link below show many examples of the the early USGS bench marks from the "Deadwood Datum" of the Black Hills of South Dakota. These photos will give the searcher an idea of what to look for and has examples of the early USGS bronze tablets, iron posts, and copper bolts.

DEADWOOD DATUM



CONTACT


© Jerry Penry 2013