Triangulation Station with scaled coordinates

[+LSUFan]

Howdy Everyone. We encountered something yesterday that I was needing some advice on, which is a triangulation station with "scaled" horizontal coordinates.

 

From what I can piece together from reading the datasheets, but I may be wrong:

 

1. There was an original triangulation station named Monroe East Base 1931

 

2. The surface mark was replaced over the 1931 underground mark in 1966 and renamed Monroe E Base Reset CP1793. This reset used the original reference marks 1 and 2 from 1931, as well as setting a 3rd reference mark at this time. This is also the triangulation station that has "scaled" coordinates, according to the datasheet. This datasheet has the marker as a triangulation station, but it doesn't have a box score like one.

 

3. This surface mark was AGAIN replaced in 1971 over the same 1931 underground mark, then still called Monroe E Base Reset AA9071. Reference marks 1 and 2, as well as reference mark 3 from 1966 were used in this 1971 reset.

 

I am kinda confused as to why CP1793 has scaled coordinates, since it was placed over the same underground mark as AA9071 was in 1971 with adjusted coordinates. I thought all triangulation stations had adjusted coordinates (or at least all the ones I have found so far have).

 

I am also kinda wondering why CP1793 is still even listed, since AA9071 was reset in it's place.

 

Any advice would be appreciated. Thanks

Edited January 2, 2011 by LSUFan

[southpawaz]

It looks to me like the crew that did the reset in 1966 was running a level line (see CP1785 one mile east, and CQ2402 one mile west), and they were probably not equipped to confirm the horizontal coordinates beyond resetting it above the underground mark, which may not have met standards. I see that the CP1793 datasheet, while calling out the reference marks in the description, does not have a box score with accurate azimuths to them. It looks like the 1971 crew did an additional check of the distance to MONROE WEST BASE to confirm the location and "regain" the horizontal accuracy.

[AZcachemeister]

My guess is that the 1966 crew found Monroe East Base disturbed/damaged, decided to reset it (CP1793), but didn't have the time or resources to actually occupy it. Since it hadn't been occupied, it couldn't yet have an adjusted location. Given that it was right over the underground mark, it was certainly 'purty durn close'.

 

The 1971 crew came along prepared to actually do the occupation, but the dang thing had got bumped again, and needed another reset (AA9071).

Then AA9071 was actually occupied in 1973, and achieved adjusted status.

 

Not the first time I have seen 'residual' datasheets for marks that have been reset, and in fact they are not really uncommon here in AZ.

[kayakbird]

CP1793''THE STATION WAS VISITED 8-4-66 AND THE STATION SURFACE MARK

CP1793''WAS FOUND DISTURBED AND THE DISK GONE. A NEW DISK WAS SET

CP1793''IN THE MONUMENT AND PLUMBED OVER THE UNDERGROUND MARK WHICH WAS

CP1793''FOUND IN GOOD CONDITION. REFERENCE MARKS NO. 1 AND NO. 2

CP1793''WERE FOUND IN GOOD CONDITION.

 

My reading of the 1966 description tells me that they re-planted the original post (saving concrete!)

with a new disk affixed in the old stem hole and it settled out of plumb. Which led to the 1969 remark:

 

CP1793'ABOVE THE SURFACE OF THE GROUND. NOTE-- THE ELEVATION OF THIS MARK

CP1793'SHOULD BE USED WITH CAUTION.

 

This one is not flat,

 

 

AA3923

but likely within the published elevation accuracy, AA3923* NAVD 88 - 989.93 (+/-2cm) 3247.8 (feet) VERTCON,

or at least better than OX0679 ETNA was.

 

kayakbird

[+LSUFan]

Thanks for the help, everyone. I am a little better educated thanks to you.