Chihuahua (state)
The Treaty of Guadalupe Hidalgo, signed on February 2, 1848, by American diplomat Nicholas Trist and Mexican plenipotentiary representatives Luis G. Cuevas, Bernardo Couto, and Miguel Atristain, ended the war, gave the U.S. undisputed control of Texas, and established the U.S.–Mexican border of the Rio Grande. As news of peace negotiations reached the state, new call to arms began to flare among the people of the state. But as the Mexican officials in Chihuahua heard that General Price was heading back to Mexico with a large force comprising several companies of infantry and three companies of cavalry and one division of light artillery from Santa Fe on February 8, 1848, Ángel Trías sent a message to Sacramento Pass to ask for succession of the area as they understood the war had concluded. General Price, misunderstanding this as a deception by the Mexican forces, continued to advance towards the state capital. On March 16, 1848 Price began negotiations with Ángel Trías, but the Mexican leader responded with an ultimatum to General Price. The American forces engaged with the Mexican forces near Santa Cruz de los Rosales on March 16, 1848. The Battle of Santa Cruz de los Rosales was the last battle of the Mexican–American War and it occurred after the peace treaty was signed. The American forces maintained control over the state capital for three months after the confirmation of the peace treaty. The American presence served to delay the possible succession of the state which had been discussed at the end of 1847, and the state remained under United States occupation until May 22, 1848.

Q: How long did the U.S. continue to maintain control over the state capital after the treaty?
three months