Summit Benchmarks

[4000'er]

I will be teaching 7th grade science next year. In one of the units the kids learn about topo maps.
I'd like to gather a collection of summit benchmark pictures of peaks for that unit.
Do you have any close-up photos of USGS Benchmarks you would like to share? I would appreciate it
You can email me directly, and I will post which ones I have received.
Thanks
Here is an example of what I am looking for...

 

[skibones]

Why do some peaks have these and others do not??

 

[4000'er]

This is just speculation...
They don’t need benchmarks on all the mountains. By using triangulation and leveling techniques they can determine the height and location of the surrounding peaks.

 

[adamiata]

I threw a few of my pictures of benchmarks into a webshots album. YOu can find them here: http://community.webshots.com/album/552304427efFFkJ

This is my favorite one. I took it at Bright Angel Point on the North Rim of the Grand Canyon at sunset.

 

[JasonPatrikz]

bench marks

Pm me your email and i can send you a couple, isolation and such. Jason

 

[Tom Rankin]

Pm me your email and i can send you a couple, isolation and such. Jason

I've got lots, I'll send in a day or 2...

 

[4000'er]

Names

Thanks for those who have already sent me pictures. If I could just ask that you identify them (which peak), that would be great.

Thanks again

 

[Papa Bear]

I have a number of pictures which I can send when I get home, including a few from the past week.

I couple of points on these disks:

1) disks on mountain tops (usually but not always set by the USGS) are generally "triangulation stations" (horozontal control) not bench marks (vertical control). The are all called "benchmarks" (one word) but us amateurs, but technically only the vertical (e.g. elevation) marks are true bench marks (two words). The triangulation stations will have a little triangle in the center, the bench marks will have a cross.

2) USGS set the marks for map control. By knowing exactly where certain mountain tops are located they could use these as fixed points when they made the maps from aerial photos.

3) The disk may not be at the actual summit if there were a better point (perhaps an outcrop to one side) that would allow viewing the nearby stations with their equipment.

4) Observations were generally done at night sighting on lights. Much easier and more exact. Think about how you would observe a pole on a peak 10 miles away in the daytime.

5) True bench marks were established by levelling from one station to the next. A pole would be placed over a mark and a levelling telescope would site it from a nearby point, and on and on. Generally these points were not more than about 200 yards apart, although most were intermediate marks and no disks were mounted at these intermediate points. Usually they would scratch a cross on some rock and move on to the next point. They would level in both directions and also do a complete loop, and then minimize the closing error over all the stations. As you might guess, it would be extremely hard to level up to a mountauin top.

4) Contours on maps are usually derived from aerial photos, and elevations computed using photogrammetric methods, a "triangulation" of sorts using photos taken from different angles. A few true bench marks would provide control.

 

[Nate]

Papa Bear, thank you for the explanation of how map data is generated. I'd been wondering about this for awhile. Considering the USGS maps depict elavation contours, I was kind of wondering if a poor surveyor had to walk these contour intervals on each mountain in order to determine where they are. I'm glad to learn that the process isn't that painstaking. But, if the process is dependent on aerial measurements, what did cartographers do in the days before planes and satelites? Does that mean that back in the day the elevations of a bunch of mountains weren't known?

 

[Tom Rankin]

But, if the process is dependent on aerial measurements, what did cartographers do in the days before planes and satelites? Does that mean that back in the day the elevations of a bunch of mountains weren't known?

Certainly. There are 4 ADK 46-R high peaks that are < 4000' for example. Cartographers have had access to increasingly more sophisticated equipment over the years. At first, they just made educated guesses. Some old maps of the Whites are laughable compared to today. Then they started to climb to the peaks and take measurements (like Verplank Colvin), and used trigonometry to calculate heights. Today, there are lasers, satellites, etc. available for ever increasing accuracy.

 

[nartreb]

An online collection of photos for those interested in seeing more.

 

[4000'er]

An online collection of photos for those interested in seeing more.

Great link,
Thanks

Keep the pics coming...

You guys are a great help.

 

[Tom Rankin]

Here is an example of what I am looking for...

Wow, I should take my marker pictures from that angle, they look so much more 3D that way!

Thanks!

 

[Tom Rankin]

http://ViewsAndBrews.com/temp - has about 20 markers from all over the place, of various kinds. I thought I had more. Oh well, gotta keep taking more pics!

 

[Papa Bear]

An online collection of photos for those interested in seeing more.

Nice set of pictures.

But one picture introduces a new issue: Look at the High Point marker. It does not have a triangle, it has an arrow. This is not the triangulation mark for High Point (NJ), it is a reference mark which in turn points to the actual High Point mark. Look at the closeup and on the rim it says "U.S.COAST & GEODETIC SURVEY REFERENCE MARK". The Coast & Geodetic Survey typically set marks for commerce whereas the USGS set theirs to make maps. Different government agencies.

From what I have read on the Geocaching Benchmark hunting web site (click on this) the actual High Point station mark is missing and only it's 3 reference marks remain.

Many triangulation stations have one or more reference marks. Trus bench marks never have any.

 

[4000'er]

I have a number of pictures which I can send when I get home, including a few from the past week.

Thanks Papa Bear.

Good info

 

[Tom Rankin]

4000'er, any chance you could make the whole set available when you're done ?

P.S. If you want fire tower pictures, I have a ton of those too, but they sort of all look alike after you sit thru a long presentation on that sort of thing.

Hmmm, come to think of it, that might happen with these markers too!

 

[arghman]

from the Horn, just north of Mt Cabot:

 

[Tom Rankin]

from the Horn, just north of Mt Cabot:

Hey, some one stole my boots.



That's a nice marker! It looks like gold!

 

[tgoodwin]

An interesting thread. Papa Bear has provided some great information, so I will just add a bit from my experience working briefly with the USGS here in the Adirondacks and on Cape Cod. When surveyors go to set benchmarks, they follow a line, setting some mark at least every mile. If you look carefully at a map, you can follow the various lines they followed. If you see "BM" and an elevation, they placed a brass disk there. If you just see an "x" and an elevation, then all they did was chisel a mark on a rock. Most bench marks also have a chiseled square nearby as a reference mark.

For instance, starting down the Adirondak Loj Rd. there are both chiseled squares and bench marks to South Meadow. Here the line splits with one branch going over Klondike Notch and down to Keene Valley where it joined the line following Rt. 73. The other branch headed to Marcy Dam and then over Lake Arnold Pass to Feldspar where it joined a line that was run up through Panther Gorge and over Four Corners. with Papa Bear's link to the descriptions for benchmarks it should be possible to find many of the ones you see on the map.

With the mapping technology available in the mid-70's, we would locate a many of these bench marks as possible. We would then "identify" them by finding a nearby feature visible on the aerial photos, and running a short line to that "picture point" to put an elevation on that point on the photo. This greatly aided the technician who actually drew the contour lines.

With regards to the reference mark at High Point, Marcy originally had a main mark and two reference marks, but only one reference mark remains. Cascade and Hurricane, however, are two of the Adirondacks that still have intact triangulation stations.