After considerable research, I can describe the location of the LAMSUS tripoint
between Louisiana, Mississippi, and federal waters.
In their 1985 decision on the historic internal waters status of the Mississippi
Sound, the Supremes ordered the Special Master to consult with the states of
Mississippi and Alabama and the US to devise the seaward boundary of those
states pursuant to their decision. That was accomplished by 1988, but the
Master balked at making the stitch between the Mississippi boundary 3nm south of
the Sound's barrier islands and the already determined boundary of Louisiana.
He did so on the grounds that the stitch was unrelated to the question most
recently before the court (whether the Mississippi Sound was internal), and
therefore beyond the authority of the Court's referral to him. The Supremes
agreed, issuing final decree in the Alabama boundary, and in that of Mississippi
as far as the Master had gone. However, they granted Mississippi and the US
leave to file a separate complaint as to their respective claims to "any
undecided portion of Chandeleur Sound." This would result in getting the stitch
made.
Pursuant to that leave, Mississippi and the US readily agreed upon a solution
and presented it to the Supremes for their approval. This was granted in the
decree Mississippi v. U.S. On Bill of Complaint (1990) at 489 US 16. The decree
says:
_________________
..the following line is stipulated by the parties to henceforth represent and
permanently mark the line from which Mississippi's Submerged Lands Act grant is
measured:
A straight line from a point on the southern shore of the most westerly segment
of Ship Island where X = 463004.481 and Y = 196885.896 in the Mississippi plane
coordinate system, east zone, and X = 2752646.58 and Y = 568331.88 in the
Louisiana plane coordinate system, south zone, to a point near the northern tip
of the most northerly of the Chandeleur Islands where X = 2775787 and Y = 513796
in the Louisiana plane coordinate system, south zone, so far as said line lies
on the Mississippi side of the Mississippi-Louisiana boundary.
_________________
The effect of this is to draw a closing line across the northeast mouth of the
internal waters of Chandeleur Sound from the nearest point on the south shore of
Ship Island south-southeastward to the north point of the Chandeleur Islands in
Louisiana, and then give Mississippi 3nm out from that baseline.
This is the same closing line that had been used as the baseline from which to
measure Louisiana's 3nm line in the final one of its boundary decrees.
Thus, if you will go to the Official Map of Louisiana 2000, at
http://www.avenza.com/MPcomp/2001/maps/GenPurp_Snead.jpg
you will find the LAMSUS tripoint at the place where the depicted Louisiana
boundary comes to an obtuse angle north of the northern end of Chandeleur
Island. The MSUS boundary (not shown) would go north-northwestward from this
point until it reached the 3nm arc from Ship Island.
Whew! I hope that's done.
Lowell G. McManus
Leesville, Louisiana, USA