Answer: GOLD
James Marshall's discovery of gold at Sutter's Mill in California in 1848 led to a "gold rush" in the decade that followed, with 1849 seeing a huge influx of people to California. (Thus we refer to the '49ers.) The swift settlement of California added incentive to build a transcontinental railway. The Pacific Railroad Act of 1862 established the charter for doing that. The First Transcontinental Railroad was completed in 1869, thus making travel and settlement into California even more accessible.
