Yellowstone Benchmark

I tell people they are what hold the world together. After the blank stare, I explain a bit about what it took before GPS to keep track of where you really were in the world.

Sometimes they'll say something about just needing a compass to know where north is, isn't that enough? So, I tell them that the compass is telling them they are south of somewhere. Which somewhere: Seattle, Denver, Chicago, Detroit, Boston?

I love it ....

height to the thousandth! Give me a break!

ok- go ahead and prove

[sarcasm]that 6239.216 WASN'T the true elevation in what ever datum of that point in 1923, perched on the Yellowstone caldera.... [/sarcasm]

ok- go ahead and prove

The vertical datum in 1923 was referenced as the 4th General Adjustment of 1912. It was replaced by the Sea Level Datum of 1929, now call the National Geodetic Vertical Datum of 1929.

ok- go ahead and prove

So the original datum was over a hundred years ago. Nice. 90 year old monument still looks pretty good. Can't imagine how many man hours it took to transfer the elevation up there.

While I was there I had a barometer on my watch that I've checked at different locations and usually I'm no more than 100' out from the published elevations and often less. But while in Yellowstone and the Continental Divide I couldn't hit it for 200' - 300'! Which even after I adjusted for the local pressure and went to the next station it would be off another 100' to 200'. So trying to figure it out.
Maybe just normal weather inversions at that altitude.:-S

So Which Dimple Do You Hold ?

That one in the middle has a line through it meaning it is no good.

I see 8 other dimples, so which one is right?

Paul in PA

http://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=PY0160

PY0160* NAVD 88 ORTHO HEIGHT - 1903.109 (meters) 6243.78 (feet) ADJUSTED

PY0160 NGVD 29 (08/20/92) 1901.880 (m) 6239.75 (f) ADJUSTED

It's a little unusual to see a C&GS disk with a stamped elevation. They mostly stopped doing that because of confusion over which datum it represented. The USGS stamped elevations much later/more often.

The dimple is also unusual since the disk is a vertical bench mark only according to the data sheet. Someone added the dimple, since the circle-and-line casting didn't have a dimple (per illustrations in George Leigh's paper on history of designs). This data sheet originally had no horizontal position, was given coordinates scaled from a map during the digitization of the NGS data, and was upgraded to Handheld precision in the last few years.

So Which Dimple Do You Hold ?

The dimple between the bench and mark. Clearly it's an update of the dimple near the center.

So Which Dimple Do You Hold ?

Do we know for certain the decimal point and dimple are not one in the same?!! That's why I do not like simple dimples. They can be confused with decimal points, dots on I's, etc.
Avoid the simple dimple.

Screw all that dimple noise!!!!

thanks to SurveyorConnect.com, I've achieved Enlightnement- A DIMPLE EPIPHANY if you will! My new policy would be to take a reflectorless topo shot on that baby and estimate another .3' in to the center, and drive on! then IF I decided to adjust my survey data I'd just place all my error in that shot since it's position really doesn't matter!

this is such a liberating feeling!!!

So Which Dimple Do You Hold ?

There needs to be a special dimple used so there's no confusion. Stamp an arrow to point to it or something

Ooops, I Missed That Dimple

I may have to hold it, since it is the biggest.

In surveying, as in sex, size does matter.

Boy this precise surveying business requires hard choices.

Paul in PA

Ooops, I Missed That Dimple

I propose we all have our own unique dimple. Upon licensure, you will be given a dimple stamp that is all yours. No more willy-nilly dimples. If we want to be treated like professionals, we need to own up to our dimples!

Here is what a sample non-simple dimple monument might look like:

Heights Stamped on USC&GS BMs

USC&GS discontinued stamping the heights on bench marks in the mid-1930s. Differences with respect to the 1912 datum was a part of the reason, but the bigger issue was because by then the vertical control loops were starting to be densified and they found with subsequent observations of marks, improvements in leveling technology and procedures, regional readjustments and updates to national vertical control standards that the heights of marks as stamped were in conflict with the most current adjusted values and this was causing confusions about what was the most reliable height value.

Heights Stamped on USC&GS BMs

Many years ago I had a fellow tell me he knew the altitude above sea level near his house because he had seen one of these BM's and it said something like 1953. Really burst his bubble when I told him the truth. First, that was the year they set it. Second, the highest point in the entire county is a hair under 1200 feet. He was somewhere closer to about 950.