What is now California was explored by various Europeans during the 16th and 17th centuries eventually being claimed by the Spanish Empire. The area then became part of Mexico in 1821 following the war for independence but was ceded to the United Staes in 1848 after the Mexican-American War.
Amazing how many wars seem to be necessary to keep human beings from doing more constructive activity!
In 1848 people began to swarm in to California to seek their fortune after gold was discovered.
HERE is a short trailer for Charlie Chaplin's THE GOLD RUSH.
Here is a full length version of THE GOLD RUSH if you have the time.
And HERE is a simple youtube cartoon that paints the picture in broad strokes.
And so begins the long saga of the country's pilgrimage of people to California to find gold in whatever form they imagine it.