In the map shown above, what does the small region below the Mexican Cession represent?

A:  Land gained during a revolt against Mexico known as the Bear Flag Republic

B: Land that had not yet been organized by the end of the Mexican-American War

C: Land gained by the United States as a result of the Treaty of Guadalupe-Hidalgo

D:  An area purchased by the United States to settle arguments over money owed to Mexico