Mexico considered the US annexation of Texas to be a hostile act and invaded across the Rio Grande in May 1846. The US counterattacked and within a year occupied much of Mexico including Mexico City. The war ended with the Treaty of Guadalupe Hidalgo in 1848. In the treaty, Mexico agreed to sell what are now California, New Mexico, Arizona, Nevada and parts of Utah and Colorado to the United States. The negotiators based the treaty on the faulty Disturnell map and the wrangling over the exact border continued for an additional five years. In December of 1853, the Gadsden Purchase resolved the controversy and established the current border.

This map is a reproduction of the famous map referenced in the Treaty of Guadalupe Hildalgo that ended the US-Mexican war. It was full of errors including placing El Paso about 300 miles from its actual location. This led to five years of negotiations and finally the Gadsden Purchase in 1854. The coast of California also shows many discrepancies and includes an explanation. It is, according to a note, (the red dot) based on reports from 1755. The number of islands off the coast (blue dot) is fancifully large and the harbor at Los Angeles is huge. Note however that the line between the Mexican provinces of Baja California and Alta California (green dot) is clear and in the treaty became the international boundary.