Before dawn on Sunday, June 14, 1846, thirty-three Americans, already in rebellion against the Alta California government, arrived in Sonoma. Some of the group had traveled from the camp of U.S. Army Brevet Captain John C. Frémont who had entered California in late 1845 with his exploration and mapping expedition. Others had joined along the way. As the number of immigrants arriving in California had swelled, the Mexican government barred them from buying or renting land and threatened them with expulsion because they had entered without official permission. Mexican officials were concerned about the coming war with the United States coupled with the growing influx of American immigrants into California.