<P> The Pacific states are the most geologically active areas in the United States . Earthquakes cause damage every few to several years in California . While the Pacific states are the most volcanically active areas, extinct volcanoes and lava flows are found throughout most of the West . </P> <P> 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 . </P> <P> One of the largest migrations in American history occurred in the 1840s as the Latter Day Saints left the Midwest to build a theocracy in Utah . </P> <P> Both Omaha, Nebraska and St. Louis, Missouri laid claim to the title, "Gateway to the West" during this period . Omaha, home to the Union Pacific Railroad and the Mormon Trail, made its fortunes on outfitting settlers; St. Louis built itself upon the vast fur trade in the West before its settlement . </P>

Map of the western side of the united states