The lands you are probably referring was the Mexican Cession (most of the US western lands now). That cession happened after the Mexican war that ended in the treaty of Guadalupe-Hidalgo signed in 1848. So the map mostly accurately reflects that as US territory in 1850.
The lands you are probably referring was the Mexican Cession (most of the US western lands now). That cession happened after the Mexican war that ended in the treaty of Guadalupe-Hidalgo signed in 1848. So the map mostly accurately reflects that as US territory in 1850.