The Western United States has been populated by Native Americans since at least 11,000 years ago, when the first Paleo-Indians arrived. Pre-Columbian trade routes to kingdoms and empires such as the Mound Builders existed in places such as Yellowstone National Park since around 1000 AD. Major settlement of the western territories developed rapidly in the 1840s, largely through the Oregon Trail and the California Gold Rush of 1849. California experienced such a rapid growth in a few short months that it was admitted to statehood in 1850 without the normal transitory phase of becoming an official territory.