<P> In the Winter of 1845 -- 46 , the federally commissioned explorer John C. Frémont and a group of armed men appeared in Alta California . After telling the Mexican governor and the American Consul Larkin he was merely buying supplies on the way to Oregon , he instead went to the populated area of California and visited Santa Cruz and the Salinas Valley , explaining he had been looking for a seaside home for his mother . Mexican authorities became alarmed and ordered him to leave . Frémont responded by building a fort on Gavilan Peak and raising the American flag . Larkin sent word that Frémont 's actions were counterproductive . Frémont left California in March but returned to California and took control of the California Battalion following the outbreak of the Bear Flag Revolt in Sonoma . </P>
who led the american forces that helped seize california from mexico
the federally commissioned explorer John C. Frémont