The Republic of Lower California was established by American filibuster William Walker in the Baja California Peninsula, part of Mexico. The declaration of independence from Mexico was made in December 1853 and abolished on 10 January 1854 when the Republic of Sonora was established.
Established on January 18th 1854 by William Walker, the Republic of Sonora was to be composed of two states. The first, Lower California, was briefly seized from the Mexican government by Walker and his impromptu mercenary band of 45 Californians and some 200 locals-the infamous 'Immortals' at La Paz, on November 3rd 1853. The neighboring Mexican territory of Sonora was envisioned as the second state and was prematurely promoted as such by Walker's personal decree on the 18th of January, 1854. Walker's successive failures to invade and capture Sonora prompted the Mexican government to run him out of Baja California and restore order to the peninsula.
Had Walker succeeded he would have been president; his partner, Watkins, vice-president; and Emory, secretary of state of the Republic of Sonora (and in the same fashion as the Republic of Texas, merely await annexation by the United States).