The Lewis and Clark Expedition, notwithstanding its merits as a feat of exploration, was also the first tentative claim on the vast interior and the western seaboard of North America by the United States. It set in motion the great movement west that began almost immediately with the first commercial overland expedition funded by John Jacob Astor’s Pacific Fur Company and would continue with the establishment of the Oregon Trail and California Trail. 

The westward movement of Americans in the 19th century was one of the largest and most consequential migrations in history, and as it so happened, paths across the West were being formalized and coming into use right around the time gold was discovered in the lands that became California in January 1848. 

Located thousands of miles away from the country’s power centers on the East Coast at the time, the announcement came a month before the Mexican-American War had ended, and among the very few Americans that were near the region at the time, many of them were army soldiers who were participating in the war and garrisoned there. San Francisco was still best known for being a Spanish military and missionary outpost during the colonial era, and only a few hundred called it home. Mexico’s independence, and its possession of those lands, had come only a generation earlier.