Lovely field day today in Central Texas and lovely project, too, a 177-acre lot in an 1877-vintage subdivision. The last resurvey of which I'd found a record for the lot that is the subject of my work was in 1938. In examining the project on aerial photography, I'd marveled that it looked as if the 1938 resurveyor's calls placed the SW corner of the tract about 210 ft. from the corner of fences that ran in the general vicinity of the West and South lines of the tract.
Well, on the ground, sure enough we did find the pipe set by the 1938 resurveyor for the SW corner of the 177-acre lot, or rather, the metal detector did. The corner fell inside the pasture, well away from the fences, and the odds of the pipe still being there didn't look that great at first impression. The shovel disclosed that the 1-1/4 in. i.d. x 48 in. pipe had been run over by machinery and the top section was separated from the base. There were about 30 inches of pipe still in the ground, plumb and straight, however, so we were able to rehabilitate the 1938 boundary marker, adding a 48 in. rod and cap monument to it to give it an exact reference point.
Sure enough, the 1938 surveyor's location of the lot corner as marked by the mangled pipe fell almost 220 ft. distant from the corner of a wire pasture fence that had apparently been built some time between 1938 and 1961. What was beside the railroad tie fence corner post? Why, of course a 1/2 in. iron pipe that had evidently been placed in 1961 by a surveyor resurveying the adjacent lots.
The somewhat unusual detail is that the private records of both the 1938 and 1961 surveyors still exist. I've already examined the field book and report for the 1938 work and have learned that the lines of the lot weren't apparently fenced at that time. The other great detail is that there is a chance that the original limestone monument from 1877 still exists. Can't ask for more interesting work or better weather.
The 1938 surveyor's field book indicates that he tied to at least one of the original limestone lot corner monuments of the 1877 subdivision of about 4,300 acres in which the lot I'm interested in is situated. He used an old fence to get his bearing basis and found that it agreed well with such old occupation as was in the vicinity of the lot in 1938.
One early exercise is to see how well his bearing basis fits what one would predict on paper for the original survey of the subdivision run in 1877 at a variation of 10°00'E. This is done so:
The National Geophysical Date Center has an online model of historical declination in the US at this link:
http://www.ngdc.noaa.gov/geomagmodels/USHistoric.jsp
That model estimates that the mean magnetic declination in the vicinity of the project in 1877 was 9°04' East. I haven't found a record of the variation that the 1877 surveyor was using yet, but 10°00'East was a pretty common value widely used at that time. So, just trying that on for size:
+09°04' True Az Mag North 1877
-10°00' Survey Variation
-------
-00°56' True Az Survey North
-00°36' Mapping Angle
-------
-01°32' Grid Az Survey North
So, the NGDC model's estimate means that "North" as used by the 1877 surveyor would have an approximate grid azimuth of -1°32' in the vicinity of the project.
By comparision, the 1938 surveyor was using a "North" with a grid azimuth of about -2°18'.
Very nice that the 1938 surveyor set such a substantial monument. When are you going to search for the limestone monument?
Are there a lot of owners living in this area? I am curious if you are going to be finding a lot of newer monuments between the 1938 pipe and the limestone monument. Gotta be interesting to see how things are (not going to) fit.
> Very nice that the 1938 surveyor set such a substantial monument. When are you going to search for the limestone monument?
I'm probably going to wait a bit to hunt for the limestone. In the meantime, we'll be looking for some other stuff that ought to narrow the search area a bit. In theory.
