42° N
Adams-Onís Treaty · Latitude 42 North
The boundary written into Article III of the 1819 treaty between the United States and Spain: from the source of the Arkansas River "in latitude 42 north; and thence, by that parallel of latitude, to the South Sea" (the Pacific).
In 1819 John Quincy Adams and the Spanish minister Luis de Onís drew a line across North America. Article III of their treaty runs the border up the Red and Arkansas rivers and then turns west along one line of latitude: "latitude 42 north," all the way to the Pacific. The treaty took effect in 1821. That same parallel still marks where California and Nevada end and Oregon and Idaho begin, and where Utah meets Idaho.
What it supports
The number 42 is written into the treaty itself, four times in Articles III and IV: "in latitude 42 north," "north or south of latitude 42," "the said parallel of latitude 42," and "the line of latitude 42, to the South Sea." It was chosen on purpose as a boundary, not measured after the fact. The Oregon Encyclopedia quotes the same Article III line and tells how Oregon Country's southern line was fixed in 1821 and surveyed in the 1860s.
What it does not
The line on the ground does not sit exactly on 42°00′. Daniel G. Major was hired in 1868 to mark the parallel. Later surveyors found his line wandered north and south of the true parallel, and the states kept that line. So the plate is the treaty's 42, not a surveyed 42.000°. Not every latitude 42 coordinate is a door (a town that happens to sit near 42°N is not this object). Not Douglas Adams; the Adams here is John Quincy Adams.
ExactnessExact
Form42
Unitdegrees of latitude
Strengthhard
When1819
Hung13 October 2026