California: Polity Style: 1846-1849

17 Aug 1846	the territory of California, formerly part of Mexico, is declared a possession of the United States in accordance with a proclamation of the Commander-in-Chief and Governor of the Territory of California issued on 17 Aug 1846 at Ciudad de los Angeles (Californian, No. 4, 5 Sep 1846, p. 2) [1]
30 May 1848	the territories of Mexico occupied by the armed forces of the United States are incorporated within the boundaries of the United States as defined by the treaty concluded between the plenipotentiaries of both nations at Guadalupe Hidalgo, Mexico, on 2 Feb 1848 (effective upon the exchange of ratifications at Querétaro on 30 May 1848) (Statutes at Large, 9:922-943; Correo Nacional, No. 121, 9 Jun 1848, pp. 1-4) [2]
12 Dec 1849	the Constitution of the State of California is adopted by the Constitutional Convention held at Monterey on 11 Oct 1849, signed by the delegates of the Constitutional Convention on 13 Oct 1849, and ratified by a popular vote on 13 Nov 1849, the results of the vote are certified by the proclamation of the Governor of California issued on 12 Dec 1849 (California Constitutional Convention 1849, pp. 459-461, 476; Alta California, No. 7, 24 Dec 1849, p. 3)

In 1846, the armed forces of the United States occupied the northern region of Mexico, including the northern part of the Departamento de las Californias (formerly the Territorio de Alta California). The area was referred to in the proclamation as the "Territory of California," although it was never formally organized as a United States territory under federal law.
The Treaty of Guadalupe Hidalgo did not specifically refer to the occupied territories as a "cession," instead defining new boundaries between Mexico and the United States.