If you click on Mexican session map from Wikipedia it should enlarge to see the area in the Mexican Session to the U.S. in 1848

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Area Mexico ceded to the United States in 1848, minus Texan claims. The Mexican Cession consisted of present-day U.S. states of California, Nevada, Utah, most of Arizona, the western half of New Mexico, the western quarter of Colorado, and the southwest corner of Wyoming.

begin partial quote from:

https://en.wikipedia.org/wiki/Mexican_Cession

The Mexican Cession is the region in the modern-day southwestern United States that Mexico ceded to the U.S. in the Treaty of Guadalupe