Until the 1840s, most of the small number of Americans in California were sailors, traders or pathfinders. What few American settlers there were had most likely come by sea, around the Horn. But beginning in 1841, large numbers of Americans set out from Missouri in wagon trains for the long and dangerous trip west. Many of these people were inspired to make the journey by the writings of John Marsh, whose articles extolling the beauty and abundance of Alta California had been published in many Eastern papers. It is estimated that by 1845, there were more than 800 Americans in Alta California, more than enough to concern the Californio families.
The ambitious and aggressive Americans were viewed as a threat to the established order. Although land ownership was limited by law to those who held Mexican citizenship and were Catholic, many Americans got around this simply by taking the necessary oaths and converting - at least in name. In the fall of 1845, however, rumors circulated throughout Alta California that the Mexican authorities would soon disallow any further conversions. Also, word spread that Mexico was planning to expel all American settlers once the spring thaw cleared the passes in the Sierra Nevada mountains.
Among those particularly upset by these rumors were the more than one hundred members of the Grigsby/Ide party. They had just completed the overland passage, arriving in the Sacramento Valley only to hear that the Mexican government was about to expel them. While the frustrated Grigsby-Ide settlers were fulminating at Sutter's Fort, there arrived at the fort one Capt. John C. Fremont, of the U.S. Army Topographical Engineers. Captain Fremont was on a mission of exploration and mapping for the U.S. Government, and had with him a patchwork crew of draftsmen, trappers, irregular solders, Plains Indians, and frontiersmen, including Kit Carson. Many historians claim that Fremont was also charged with fomenting whatever trouble he could in California - including, perhaps, himself spreading the rumors about a Mexican plot to expel Americans - to goad Mexico into attacking the settlers. This would allow the U.S. military to sieze California in order to "protect" American lives and property.
It is probable that Fremont mischievously "inspired" members of the Grigsby/Ide party to move against Sonoma and take the land Mexico would not sell them. The risk in such a move must have been withheld from the small band of settlers; even with just fifty residents, Sonoma was second only to Monterey in population. Mexico might decide to crush any independence movement to keep it from spreading. The U.S. military - however ready it might be - was far away; only a few naval vessels were close by, and these might prove difficult to contact. But the Mexican authorities were in a similar situation: Monterey and San Francisco (then called Yerba Buena) were still rather small settlements; Los Angeles was one dusty street and a tiny pueblo.
The gold that would bring millions to California had not yet been made known to the outside world, though the local Tulare Indians knew of it long before it was "discovered" at Sutter's Mill. Besides 7000 Mexicans and Californios, and the few hundred Americans, there were perhaps 150,000 Native Americans in Alta California. However, despite their superior numbers, the tribes in the region were suffering the ill effects immigration -- Mexican and American alike -- was having on their way of life: many of their people, lands and traditions had already been lost.