The news of actual war reached the Pacific shortly after the American population in California had begun its little revolution. Frémont was in his glory for a time as the responsible head of American power in the province. Naval commanders under their own orders coöperated along the coast so effectively that Kearny, with his army of the West, learned that the conquest was substantially complete, soon after he left Santa Fé, and was able to send most of his own force back. California fell into American hands almost without a struggle, leaving the invaders in possession early in 1847. In January of that year the little village of Yerba Buena was rebaptized San Francisco, while the American occupants began the sale of lots along the water front and the construction of a great seaport.
The relations of Oregon and California to the occupation of the West were much the same in 1847. Both had been coveted by the United States. Both had now been acquired in fact. Oregon had come first because it was most easily reached by the great trail, and because it had no considerable body of foreign inhabitants to resist invasion. It was, under the old agreement for joint occupation, a free field for colonization. But California had been the territory of Mexico and was occupied by a strange population. In the early forties there were from 4000 to 6000 Mexicans and Spaniards in the province, living the easy agricultural life of the Spanish colonist. The missions and the Indians had decayed during the past generation. The population was light hearted and generous. It quarrelled loudly, but had the Latin-American knack for bloodless revolutions. It was partly Americanized by long association with those trappers who had visited it since the twenties, and the settlers who had begun in the late thirties. But as an occupied foreign territory it had not invited American colonization as Oregon had done. Hence the Oregon movement had been going on three or four years before any considerable bodies of emigrants broke away from the trail, near Salt Lake, and sought out homes in California. If war had not come, American immigration into California would have progressed after 1846 quite as rapidly as the Mexican authorities would have allowed. As it was, the actual conquest removed the barrier, so that California migration in 1846 and 1847 rivalled that to Oregon under the ordinary stimulus of the westward movement. The settlement of the Mormons at Salt Lake developed a much-needed outfitting post at the head of the most perilous section of the California trail. Both Mormons and Californians profited by its traffic.