The American Conquest of California
Meanwhile in Alta California, the halcyon days of the Spanish colonial period had only a brief revival during the benign administration of the Mexican Governor Figueroa (1833-1835), but were never to return after his death in 1835. On 7 November 1836 the disputation or provincial assembly of Alta California issued a proclamation declaring the province a "free and sovereign state" until such time as the Mexican government would restore the Federalist Constitution of 1824. After this threat of secession, the governors of the province appointed by the Mexican government were forced to contend with a stubborn and increasingly militant demand by the native Alta Californians for "home rule" in their internal affairs. Political confrontations and armed skirmishes occurred repeatedly between the Californians and the Mexican government, and between north and south factions in the province of Alta California. The attendant intrigue and sectional dissension served to demonstrate the military unpreparedness and tenuous authority of the Republic of Mexico in Alta California. These conditions were not lost on the American, British and French navies, each of which was standing by and prepared to annex Alta California on the first convenient pretext.
Commodore Thomas Ap Catesby Jones of the American Navy was the first to move. In the fall of 1842, while keeping a close eye on the movements of French and British vessels, Commodore Jones received information which led him to believe that Mexico and the United States were at war over Texas, and that three British men-of-war were headed north toward Alta California. In light of the instructions he had earlier received to take prompt action under such circumstances, the Commodore entered Monterey Bay with two warships on 13 October and demanded surrender of the post to the United States. Governor Alvarado, citing the futility of resistance against "the powerful force" brought against him, promptly signed articles of surrender, and the American supplanted the Mexican flag over the government house at Monterey. There was no fighting or bloodshed and after a few weeks in Monterey, during which relations between the Californians and Americans were friendly, it was learned that such rumors as war with Mexico, movement of the British fleet, and cession of Alta California to Britain were all without foundation. Whereupon, the Commodore withdrew his garrison from Monterey, apologized to the Governor and, after firing a parting salute to the Mexican flag which had been restored to its rightful place over government house, sailed away. 
Commodore Jones' premature conquest of Monterey from the sea in 1842 had all the fanciful airiness of comic opera. Fortunately it did not seriously disrupt American relations with Mexico, yet it did heighten Mexican indignation and apprehension about American designs on Alta California. It was also a reminder to European nations that any intrusion by them would be forcefully rebuffed, as had been declared by President Monroe (1817-1825) in his annual message to Congress on 2 December 1823 (The Monroe Doctrine): "The American continents, by the free and independent condition which they have assumed and maintain, are henceforth not to be considered as subjects for future colonization by any European powers...."
From the standpoint of long range American objectives, immigration of settlers to Alta California now became a potentially critical factor. It was the American view that their presence in sufficient number, as in Oregon and Texas, would have a major influence on the future of the province. We have already referred to the preference shown by settlers for the Oregon Country, but favorable reports in the press began to arouse increasing interest in California. The "First Emigrant Train to California" left Independence, Missouri, on 19 May 1841 and, after incredible hardships, arrived almost six months later on 4 November at the vast Rancho Los Meganos (The San Dunes) purchased in 1837 by John Marsh and located near the base of Mt. Diablo 40 miles east of San Francisco Bay. 
This first group of immigrants to travel overland directly to California did so in response to a letter about the magnificent opportunities in California written by Marsh, who gave a detailed description of the route to be taken over the Sierra Nevada (Snowy Range). John Marsh was born in Salem, Massachusetts, in 1799 to an old and respected family with Puritan and Revolutionary roots. He graduated from Harvard with a B.A. degree in 1823. We introduce him here as he fled on horseback down the Santa Fe Trail in 1836 to avoid the creditors of his bankrupt store in Independence, Missouri. He was also seeking to evade arrest by the U.S. Army for selling guns to enemy Indians from his frontier store in Prairie du Chien, Wisconsin, during the Blackhawk War in 1832. En route to California, he was captured by the Comanches, from whom he miraculously escaped. When he arrived at last in the Pueblo of Los Angeles, he was penniless. Undismayed by his predicament, he announced that he was "Doctor John Marsh", and applied for a license to practice medicine and surgery. He had in fact gained some medical knowledge from anatomy courses that he took at Harvard, and a brief apprenticeship with Doctor John Dixwell of Boston, but he had no formal medical schooling and no medical degree. Nevertheless, he obtained a license to practice by submitting his Harvard B.A. diploma to the Mexican authorities. They believed that the inscrutable Latin in which the document was written signified that he had been awarded an MD degree by Harvard. Thenceforth he was known in California as "Doctor Marsh." Through his considerable success in medical practice in Los Angeles, and later in the vicinity of the Pueblo of San Jose and Yerba Buena, he earned enough money to purchase the extensive Rancho Los Meganos in the shadow of Mt. Diablo - after he had first met the requirements of the law by being baptized into the Catholic Church and becoming a Mexican citizen.
John Marsh has been sometimes referred to as the "first American doctor in California." With greater validity, he is credited with having had a major influence on immigration to California by his convincing advocacy of its mild and healthful climate, fertile valleys and other resources. There is much more to tell of John Marsh's life on six frontiers, a story that ended tragically with his brutal murder in 1856 by aggrieved ranch hands, but this will suffice as a glimpse of medical standards and fortune hunting in Alta California about the time of the first immigrant caravan. 
California immigrants arriving by the overland route increased yearly and in 1845 at least 250 persons entered the province. The year 1846 saw the entry into California over the Sierra Nevada of over 500 men, women and children, the greatest overland migration to date. The pioneers of '46 included the unfortunate Donner Party that set out from Sangamon County in central Illinois on 15 April to seek new homes in California. They were trapped by early snow for four months in the high Sierra at Donner Lake near Truckee, California. The survivors were rescued in the Spring of 1847 by the heroic efforts of men from Sutter's Fort near Sacramento. The total number of deaths in the Donner Party, mainly from starvation and disease, was 36. Forty-five, including five men, eight women and 32 children finally reached Sutter's Fort alive where John Sutter did all he could to restore them. The Donner experience is often cited as an example of the perils and disasters that threatened the California immigrant trains.
The name of John Augustus Sutter (1803-1880) is remembered not only for his humanitarian aid to the Donner Party, but also for his involvement in many other memorable aspects of California history. Captain Sutter, as he was called, emigrated from Switzerland to the United States in 1834. After spending four years in Indiana and points west, including Missouri where he made his declaration to become an American citizen, Sutter set out in 1838 for the Oregon Territory with a trapping expedition. While in Oregon, he conceived the idea of founding a colony in Alta California, which he eventually reached by a circuitous sea route which took him to Hawaii, thence to Alaska, and eventually to Yerba Buena, where he arrived in 1839. He obtained permission from the Mexican authorities to occupy a tract of land where the American joins the Sacramento River in the environs of the present city of Sacramento. He became a Mexican citizen and received a grant for 50,000 acres of land where he founded a colony known as New Helvetia. He also built a fort which was the center of his increasingly prosperous business and ranching enterprises. Sutter's Fort (now the site of an historic park in Sacramento) was located on the main line of overland migration and became a major trading and rendezvous point for immigrant trains coming down from the Sierra into the valley. Captain Sutter's hospitality and generous assistance earned him the gratitude of the new arrivals, and his sterling qualities of character and leadership secured him the respect of settlers and native Californians alike. Yet, by a cruel twist of fate, an excess of good fortune loosed around the Captain a tempest of lawlessness and greed that swept away his princely holdings, leaving him in his old age a pensioner of the State of California and a futile supplicant to the American Congress. 
It is impossible to know with certainty how many American immigrants came over the mountains into California during the years from 1843 to 1846, but Hunt and Sanchez believe that it was a total of about 1500, presumably counting men, women and children. It is significant that most of them were homeseekers who planned to settle permanently and develop the country, whereas itinerant trappers and traders had predominated in an earlier period. 
This is an opportune moment for a reminder of the unreliability of California population estimates during the years prior to statehood. It is not possible to reconcile the various reports on this subject. Some data seem to refer to men only, some to adults only, and some to men, women and children. No census in the modern sense was conducted. Some of the available population statistics are the guesses of contemporary observers, and some are the result of later scholarly efforts at retrospective calculation. Let us turn then for help on this question to John Marsh of Rancho Los Meganos with whom we are already acquainted. In 1846 he was regarded as being among "the most prominent men in California" according to a list provided to President Polk by Mr. Thomas Larkin who was American Consul and confidential informant (that is, intelligence agent) of the State Department living at Monterey. Larkin sought Marsh's cooperation in acquainting the American government and people with the natural beauties and resources of Alta California. Marsh obliged by writing a letter in 1846 to his friend and former patron in the Old Northwest, U.S. Senator Lewis Cass of Michigan. The letter included the following estimate of California's population: 7000 persons of Spanish descent; 10,000 civilized or domesticated Indians; 700 Americans; 100 English, Irish and Scotch; about 100 French, Germans and Italians. (These data seem to refer to male population only.) For want of a better estimate for 1846, we will accept Marsh's approximation of California population in that year as a baseline for comparison with later years. Marsh's figures are frequently quoted, and had considerable circulation in the United States at the time since Senator Cass saw that Marsh's letter was widely published. 
The fateful year of 1846 was a turning point in the affairs of Alta California. As already pointed out, the political situation in the Mexican Republic deteriorated after independence from Spain in 1823. The unstable central government was ineffectual in maintaining control over the rebellious and essentially self-governing northern province, itself the scene of internal dissension and disorder. As the caravans continued to bring in American settlers, it was forecast in the United States that the immigrants would sooner or later band together and secede - and that Alta California would go the way of Texas. Although the Americans were outnumbered ten to one in the province, predictions were that they could easily overcome the disorganized and quarreling native Californians.
At the same time, Thomas Larkin was on another tack, one presumably favored by the American government. His secret instructions were to cultivate the Californians privately, to impress upon them the political and economic advantages of requesting annexation by the United States, and to assure them that the United States would welcome such a request. We shall never know whether this covert approach would have achieved its goal of peaceful annexation of Alta California for events took another course, as we shall now relate, but only in the barest outline.
As one might expect, the Californians (i.e. the Mexican citizens of California) were agitated by the rumors of impending war between Mexico and the United States over the annexation of Texas. They were increasingly suspicious of the intentions of the growing number of American settlers who were, in turn, fearful that the Californians were planning to expel them from the province. Tension between the American settlers and the Californians was further heightened when Captain John C. Fremont, who had entered Alta California on his third exploring expedition, built a log fort on Gavilan (Hawk's) Peak not far from Monterey, and on 6 March 1846 raised the American Flag. He abandoned the fort after three days and retired to the north, but only after being confronted with the superior force of General Jose Castro, military commandant of Alta California. 
What Captain Fremont intended to accomplish by this provocative maneuver is unclear, but this and subsequent incidents led American settlers in the inland valleys to believe that an attempt by the Californians to expel them was imminent. It was also concluded by the settlers, who had not yet learned of the declaration of war against Mexico on 11 May 1846, that Fremont's presence in the area was a signal that the American government would sanction a revolt by the settlers. There followed the implausible episode known as the Bear Flag Revolution during which a party of 32 or 33 Americans, chiefly roving immigrants and hunters who had the backing of Fremont, seized the small, drowsy pueblo of Sonoma just north of San Francisco Bay on 14 June 1846. At daybreak on this quiet Sunday morning, what appeared to be a band of uncouth and menacing strangers in leather hunting-shirts entered the home of the distinguished General Mariano Guadalupe Vallejo who was arrested, required to give up the keys to public property, and taken as a prisoner to Sutter's Fort. Since the General was the respected former military commandant of Alta California, friendly to the Americans, and among the influential native Californians who favored voluntary entrance of the province into the Union, his haughty treatment during the Bear Flag incident not only inflamed the Californians, but was also an embarrassment to the United States.
The insurgents improvised a crude red, white and blue flag emblazoned with the painted outline of a grizzly bear to serve as the ensign of the Bear Flag Republic which, Texas-fashion, they formally proclaimed. This impetuous filibuster by American settlers, precipitated by the belligerent stance and encouragement of Captain Fremont, was an incredibly disorganized affair. Fortunately, no one was injured. It did, however, undermine the American government's plan being pursued by Larkin to gain the goodwill and voluntary allegiance of the Californians. They were, instead, thoroughly incensed and as a result probably mounted a more determined resistance to American forces during the imminent conquest of California than might otherwise have been the case. On the whole, the practical effect of this colorful episode on the conquest was probably not significant, although there has been considerable speculation on this point among historians.   
As for the Bear Flag Party, they gladly disbanded to join American forces and participate in the general conquest of California which soon followed. Their original flag was lost in the great San Francisco earthquake and fire of 1906, but rose from the ashes on 3 February 1911 when the Bear Flag was adopted as the California State Flag. As for Fremont, his military service in California was marked by further rash and arrogant behavior, leading to his court-martial for insubordination. The remainder of his public service was also attended by controversy. However, it should be remembered that early in his career Fremont was an intrepid and observant explorer of California and the West whose expeditionary reports were of great value. In one of these reports, he compared the entrance of San Francisco Bay to the Golden Horn of Byzantium, and gave the name of Chrysopylae or Golden Gate to the Bay's majestic inlet from the sea. Little did he suspect how vividly the felicity of his classical allusion would be affirmed by future events. 
Unwittingly, Fremont and the Bear Flag Party were at least fortunate in the timing of their revolt. On 7 July 1846, three weeks after the Bear Flag Revolution, Commodore John D. Sloat, commander of United States Naval Forces on the Pacific, upon learning that war with Mexico had begun, occupied Monterey, raised the American Flag, and issued a proclamation declaring that "henceforward California will be a portion of the United States". It was in this fashion that the United States took formal possession of California. The Spanish-speaking Californians rose in arms but in spite of their spirited and temporarily successful defensive action in Southern California, they were rapidly overcome by the American forces who took Los Angeles on 10 January 1847, thus completing the conquest of California. Later that year, at dawn on 17 September, Mexico City surrendered to the Americans. This ended the fighting in the Mexican War. As already noted, the Treaty of Guadalupe Hidalgo was signed in Mexico City on 2 February 1848, and was finally approved by the Mexican Congress on 24 May 1848.