Okay, Adam (plus Mike and anyone else paying attention), I'm back. I am
inserting my comments below.
> A while ago somebody (it might have been acroorca2002) posted about a
> trip to visit the northernmost point in mexico, which I guess under
> our notation would be something like mxn or mxus2azcabc. Anyway, I
> was planning a visit out the that area either this coming Friday or
> Saturday, and was wondering if anyone had any hints on the best ways
> to approach the point. I guess Lowell would have the goods on where
> exactly in the Colorado River the tripoint is, since he's our
> resident expert on the usmx treaty.
The current 1970 MXUS treaty says that the international boundary in both the
Colorado River and the Rio Grande "shall run along the middle of the channel
occupied by normal flow and, where either of the rivers has two or more
channels, along the middle of the channel which in normal flows has the greater
or greatest average width over its length." Note that the operative
measurements exclude depth, which is generally in short supply in these rivers.
As Mike has pointed out, the AZCA boundary runs "down the middle of the channel
of said [Colorado] river." The two descriptions are essentially in agreement.
Since this river is hardly navigable, I would tend to discount the thalweg and
lean toward the median line for each boundary. The best practical estimation
of this would probably be half of the distance between the vegetation lines on
the respective banks.
> I suppose another historical tripoint I could pick up would be the
> historical tripoint between California, New Mexico Territory, and
> Mexico before the Gadsden Purchase was made. That would be where the
> Gila River flows into the Colorado, on the north side of Yuma, right?
> Lowell, do you have any idea whether that tripoint would be in the
> river midpoint, the thalweg, one of the banks, or what?
The juncture of the two mentioned river would be the ghost tripoint; however,
both rivers show evidence of having been highly braided and meandering
streamcourses in their relevant reaches. I doubt that it would be humanly
possible to ascertain the precise point. In fact, the current AZCA boundary has
been reduced to a series of stepped surveyed lines across a former meander about
four miles in diameter called "The Island" at the mouth(s) of the Gila. I
assume that this was done (apparently post-Van Zandt) as the only practical
solution by agreement between the states and the consent of the Congress, but I
have not researched the particulars. Clearly, if the Gadsden Purchase had not
occurred, demarcation of the MXUS boundary through this same area just northeast
of Yuma would have required an innovative solution.
Lowell G. McManus
Leesville, Louisiana, USA