Analysis of information sources in references of the Wikipedia article "Adams–Onís Treaty" in English language version.
The formal name of the agreement is Treaty of Amity, Settlement, and Limits Between the United States of America and His Catholic Majesty.
Preliminary studies indicate that, as the result of an 1870 surveying error, Oregon has about 31,000 acres of California, while California has about 20,000 acres of Oregon.
The border should follow the 42d parallel straight west from the 120th meridian to the Pacific. Instead it zigzags, and only one of the many surveyor's markers put down in 1868 actually is on the 42d parallel.