At www.funcionpublica.gob.mx/unaopspf/dgapi/lgbn_c4.htm is the text of Article
49 of Mexico's General Law of National Goods, in which is delimited the ZoFeMaT.

Section I says:

"When the coast presents beaches, the federal maritime land zone will be
constituted by the strip of twenty meters of width of firm land, passable and
contiguous to these beaches or, in their case, to the shores of the rivers, from
their mouths in the sea, unto one hundred meters upriver;"

[Mike, this somewhat rearranges your concept of the "boca chica" of the Río
Grande.]

Furthermore, Section II includes in the ZoFeMaT "the totality of the surface of
the keys and reefs located in the territorial sea." Section III deals with a
20-meter strip from the annual high-water mark in "lakes, lagoons, estuaries or
natural deposits of sea water that communicate directly or indirectly with the
sea." Section IV deals with the special cases of artificial marinas or
acquicultural facilities, and I'll let you translate those for yourself if
interested.

Whenever land is gained from or lost to the sea by natural or artificial causes,
the boundaries of the ZoFeMaT move to conform to the new physical configuration
of the land.

Nowhere does this particular article of the law deny state territorial
sovereignty or jurisdiction over the ZoFeMaT, but it does place it in the
federal public domain and place its regulation, management, and exploitation
exclusively under the Secretariat of Urban Development and Ecology (since
succeeded by the Secretariat of the Environment and Natural Resources).

I'm still looking for other clarification on the question of the actual seaward
territorial extent of the states.

Lowell G. McManus
Leesville, Louisiana, USA