Local bench marks lead to more questions than answers
Monday, December 23, 2013 10:48 AM
Bench marks - have you noticed one recently? Or at all? Perhaps if you are among the crowd that does geocaching, you may be acquainted with bench marks. I've always been intrigued by the one on the exterior northwest corner of the 1904 Carnegie Library, now city hall. More curious, maybe, because the bench mark was not installed at the time the library was built, but in 1931. As you can see in the photo, it was placed there by the U.S. Coast & Geodetic Survey, showing elevation 1278.774' above mean sea level. There is also the cautionary note, "$250 fine or imprisonment for disturbing this mark." What the E 15 means, I do not know.
Bench marks very visible — on the Carnegie library building and on the Main Streeet bridge.
My son, Gene, then called to my attention another bench mark within a short distance, on the bridge abutment across the street from Marchant's Garage on West Main St. This one is set in the concrete, face up, and was installed in 1981 by the State of Minn. Dept. of Highways. It, too, has the $250 warning for disturbing its position.
Years ago the library was disposing of volumes of World Book Encyclopedia, and the set I acquired dates to 1964. It tells that a bench mark is a permanent recognizable point that lies at a known elevation. Surveyors and engineers may bury a concrete post in the ground with the brass plate on top. These folks use the information from the bench mark when planning dams, railroad stations or roads, actually measuring the vertical distance it lies from some other bench mark. That's why the two aforementioned bench marks are puzzling, as they should be about the same elevation above sea level, and yet I don't understand the numbers.
On the computer's Wikipedia, we read that bench marks are typically placed by a government agency or private survey firm and that the government maintains a register of them, available to inquiry. In the U.S., bench marks are placed by three agencies: the U.S. Coast & Geodetic Survey, as seen on the Carnegie building, the U.S. Geological Survey, and the U.S. Army Corp of Engineers. Where does the State of Minn. Dept. of Highways fit in? Other countries that place and maintain records of bench marks include Canada, France, Italy, Japan, New Zealand, Spain and the United Kingdom.
As to my inquiries locally, a visit to neighbor and retired school teacher, Don Rose, produced more clues. Rose sometimes sent his earth science eighth grade class members to check out visible bench marks. Among them might have been guys from the Class of '78 like son Gene, Kenny Clark, Jay Groth, Scott Mulholland, Tim Majors, Dan Balbach, Dave Vickmark, Kraig Weise, Dan O'Connell, Phil Sheldon, Dave Oftedahl, Mike Koebke, Delvin Drinkall, Gary Gunderson, Bob Hamre, Mark Cummings, Randy Daggett, Dan Terbeest, and many others.
Do you suppose this was an assignment or extra credit, and if the girls checked out the bench marks, too?
A call to surveyor, Jerry Schwarz, sent me to city hall where surprising information was found. The flood plain maps show a total of ten "elevation reference marks" but not the 1981 bench mark shown here. The 'reference marks' may be brass disks as shown, or a 'concrete nail' driven into the ground, or a 'chiseled square' on a concrete pipe, located in a particular spot. It is noteworthy that many reference marks are located on or near the CMSt & P railroad and the 'abandoned railroad' (Chicago Great Western), but also on or near bridges and highway intersections. In fact, four of the ten reference marks are chiseled squares on concrete pipes.
Next summer while out hiking, I have plans to see if any of these reference marks can be found by a neophyte or if they take a surveyor's skill to locate them.
Obviously there is much more to learn about bench marks or reference marks, and I have many questions.
Sincere thanks to helpful friends, neighbors, professionals, and interested folks who shared their suggestions and expertise on bench marks.
May the year 2013 have been a notable bench mark for you. Whether a good one, or not so, we have survived. We look ahead to 2014 with hope! Blessings to all this holiday season.