Proclamation 70—Defining the Boundary Between the United States and Mexico
By the President of the United States of America
Whereas, pursuant to the first article of the treaty between the United States and the Mexican Republic of the 30th day of December, 1853, the true limits between the territories of the contracting parties were declared to be as follows:
Retaining the same dividing line between the two Californias as already defined and established according to the fifth article of the treaty of Guadalupe Hidalgo, the limits between the two Republics shall be as follows:
Beginning in the Gulf of Mexico 3 leagues from land, opposite the mouth of the Rio Grande, as provided in the fifth article of the treaty of Guadalupe Hidalgo; thence, as defined in the said article, up the middle of that river to the point where the parallel of 31° 47' north latitude crosses the same; thence due west 100 miles; thence south to the parallel of 31° 20' north latitude; thence along the said parallel of 31° 20' to the one hundred and eleventh meridian of longitude west of Greenwich; thence in a straight line to a point on the Colorado River 20 English miles below the junction of the Gila and Colorado rivers; thence up the middle of the said river Colorado until it intersects the present line between the United States and Mexico.
And whereas the said dividing line has been surveyed, marked out, and established by the respective commissioners of the contracting parties, pursuant to the same article of the said treaty:
Now, therefore, be it known that I, Franklin Pierce, President of the United States of America, do hereby declare to all whom it may concern that the line aforesaid shall be held and considered as the boundary between the United States and the Mexican Republic and shall be respected as such by the United States and the citizens thereof.
In testimony whereof I have caused the seal of the United States to be hereunto affixed.
Given under my hand, at the city of Washington, this 2d day of June, A. D. 1856, and of the Independence of the United States the eightieth.
By the President:
W. L. MARCY,
Secretary of State.
Franklin Pierce, Proclamation 70—Defining the Boundary Between the United States and Mexico Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/203122