Wednesday, February 13, 2008

General Land Office

Those of you who live in the eastern part of the country don't get much opportunity to see these survey markers. The General Land Office, one of the precursor agencies to the current Bureau of Land Management, had the responsibility for conducting the cadastral survey of the western three-quarters of the country and laying out the township and range grid system used for property identification. The whole history of why and how this system was designed and implemented is a fascinating story and I would direct you to Andro Linklater's book, Measuring America

The surveyed lands were divided into square townships that are six miles on a side, 36 square miles in area. Each square mile, or "section" is identified by number, 1 to 36. In some areas of the far west (such as here) the GLO placed brass survey markers, like the one to the left of the cairn in the photo, to mark section corners.

This close-up shows the cap of the marker that tells the township, range and the four sections that meet there. Also the year the marker was placed - 1912.

Back in the day before hand-held global positioning systems, we navigated our field surveys with USGS topo maps and compasses and these sorts of markers were welcome friends that helped us find our way. Optical surveyors using transits also depended on these and most we see here are marked with cairns, wooden masts or reflective markers like you can see in the picture at top.

Highly accurate GPS systems eliminate the need for these. Each of my survey crews carries a hand-held GPS unit with sub-meter accuracy and we are totally spoiled in finding our way around. We typically check the work of the old surveyors, and my crew chief tells me that the marker you see above is about 10 feet west of where it should be.

I think that's darn fine shooting for 1912 technology, don't you?

1 comment:

Anonymous said...

Great post! Love the old school stuff.