The Cheyenne people made up one of the largest tribes in the region during the mid 19th century. Prior to the 18th century, the Cheyenne lived in the Great Lakes region until stronger tribes in that area forced them westward. Over time, the Cheyenne migrated toward the Black Hills and the Platte River valley. Eventually, the massive herds of buffalo roaming the plains lured a branch of the tribe southward across the Platte River into the Arkansas River valley of today's southern Colorado and Kansas. By the mid 1800s, the Cheyenne had totally abandoned their sedentary agricultural traditions and completely adopted the nomadic buffalo-hunting culture. They replaced their earthen lodges with tepees, and their diet changed from agricultural products to mainly buffalo meat. The Cheyenne flourished in the Arkansas River region up into the late 1840s. War between the US and Mexico in 1846, brought increased traffic onto the Santa Fe Trail, but most travelers passed unmolested through the Cheyenne territory. However, the discovery of gold in California brought hordes of miners through the Cheyenne lands. The gold prospectors were only passing through, but without realizing it, they brought cholera to the Southern Plains in 1849; the disease was devastating to the Cheyenne and may have killed more than half the Southern Cheyenne population.