--- In BoundaryPoint@yahoogroups.com, "Lowell G. McManus"
<mcmanus71496@m...> wrote:

> The geodesic segment originally terminated at the confluence of the

rivers,

> which was then somewhere in the bottoms northeast of what is now

downtown Yuma.

I believe you are correct. Checking out the City of Yuma's website
shows some old photographs that show Fort Yuma located on the bluff
on the opposite side of the Colorado, at the confluence of the two
rivers. If you look at the landforms, too, it seems more likely that
the location of the confluence changed along the floodplain there
rather than the low mesa the town sits upon.

In other words, the line started at the confluence of the two rivers,
but the border started where that line crossed the Colorado.

I wonder how the western end of that line was chosen. It seems likely
that it was just chosen as a location that allowed for the area
around San Diego Bay to be in the USA but not much more. Seems odd
that they didn't set the border on the Pacific at, say, the mouth of
the Tijuana River, which would be a couple miles north of where it is.

While we're at it, I wonder what the history of the geodetic line
that forms the WNW/ESE southern border of Arizona/Gadsden Purchase
is. How was it chosen? A map of Baja California shows Mexico Hwy. 2
extending for about 15 miles WNW of the azbcso tripoint, roughly
along the same alignment as the WNW/ESE line in question. Hmm.

Adam