Captain John C. Frémont, leading a U.S. Army topographical expedition to survey the Great Basin, had entered the Sacramento Valley in December 1845.

Frémont's party was at Upper Klamath Lake, Oregon Territory, when it received word that war between Mexico and the U.S. was imminent; the party had then returned to Alta California.

Frémont has reportedly begun agitating American settlers to revolt against Mexican rule.

After telling the Mexican governor and the American Consul Larkin he is merely buying supplies on the way to Oregon, he instead goes to the populated area of California and visits Santa Cruz and the Salinas Valley, explaining he has been looking for a seaside home for his mother.

Mexican authorities become alarmed and order him to leave.

Frémont responds by building a fort on Gavilan Peak and raising the American flag.

Larkin sends word that Frémont's actions are counterproductive.

Frémont leaves California in March but will return to California and take control of the California Battalion following the outbreak of the Bear Flag Revolt in Sonoma.

Mexico has issued a proclamation that unnaturalized foreigners are no longer permitted to have land in California and are subject to expulsion.

With rumors swirling that General Castro was massing an army against them, American settlers in the Sacramento Valley have banded together to meet the threat.

On June 14, 1846, thirty-four American settlers, apparently encouraged by the presence of the John C. Frémont-led government expedition although unaware of the Mexican war, seize control of the undefended Mexican government outpost of Sonoma to forestall Castro's plans.

One settler creates the Bear Flag and raises it over Sonoma Plaza.

The settlers establish the Bear Flag Republic (named for the grizzly bear on its makeshift flag).

Within a week, seventy more volunteers had joined the rebels' force, which grows to nearly three hundred in early July.

This event, led by William B. Ide, becomes known as the Bear Flag Revolt.

On June 25, Frémont's party had arrived to assist in an expected military confrontation.

San Francisco, at this time called Yerba Buena, had been occupied by the Bear Flaggers on July 2.

On July 5 Frémont's California Battalion is formed by combining his forces with many of the rebels.

U.S. Commodore John Drake Sloat, commander of the U.S. Navy's Pacific Squadron, near Mazatlan, Mexico, had received orders to seize San Francisco Bay and blockade California ports when he was positive that war had begun.

Sloat had set sail for Monterey, reaching it on July 1.

Upon hearing of the events in Sonoma and Frémont's involvement, Sloat erroneously believed Frémont to be acting on orders from Washington and orders his forces to occupy Monterey on July 7 and raise the American flag.

Seventy American sailors and marines occupy Yerba Buena on July 9, claiming California for the United States and and raise the American flag.

Later that day in Sonoma, the Bear Flag is lowered and the American flag is raised in its place.

Monterey-based Mexican authority José Castro travels south, apparently to reconcile with his Los Angeles-based rival Pio Pico and resist the U.S. takeover.

Frémont, on Sloat's orders, has brought one hundred and sixty volunteers to Monterey, in addition to the California Battalion.

On July 15, Sloat transferrs his command of the Pacific Squadron to Commodore Robert F. Stockton, who is more militarily aggressive.

He musters the willing members of the California Battalion into military service with Frémont in command.

Stockton orders Frémont to San Diego to prepare to move northward to Los Angeles.

Commodore Robert Stockton replaces Sloat on July 23 and sails down the coast, landing troops led by Frémont at San Diego and putting ashore an additional force near Los Angeles.

it had taken almost three months for definitive word of Congress' declaration of war against Mexico on May 13, 1846, to get to California.

American consul Thomas O. Larkin, stationed in Monterey, works successfully during the events in that vicinity to avoid bloodshed between Americans and the Mexican military garrison commanded by General José Castro, the senior military officer in California.

As Frémont lands in San Diego, ...