Colorado is one of the least geographically homogenous of the United States, ranging from the flat, endless plains of the east to the colossal mountains of the west. In the north, Native Americans hunted and trapped in lush mountain valleys in summer, and returned to the prairies for the winter; in the south, the Ancestral Puebloans of Mesa Verde grew corn on their isolated mesas and shared in the great early civilization of the southwest. Different parts of what's now Colorado accrued to the US at different times: the east and north were acquired under the Louisiana Purchase in 1803, while the south was won 45 years later in the war with Mexico . (Land grants issued under Mexican rule were honored by the Americans, which accounts for a still-strong Hispanic influence.) Gold-hungry Spaniards came through in the sixteenth century, and US Army Colonel Zebulon Pike ventured into the mountains on an exploratory expedition in 1806, but the Native American way of life only became seriously threatened with the discovery of gold west of Denver in 1858. At that time Colorado was still part of Kansas Territory; it became a territory in its own right in 1861, and a state in 1876. The distractions of the Civil War gave the Native Americans the opportunity to fight back, but they were soon overwhelmed. From then until the end of the century, Colorado boomed; the quantities of gold and silver extracted from the mountains did not really compare with the riches found in California, but they were sufficient to fuel a rip-roaring frontier lifestyle. At first, too, absentee landlords attempted to exploit massive ranches on the plains, but their disregard for conservation ensured that the droughts and storms of 1886 and 1887 swept away the topsoil. For the modern visitor, the obvious first port of call is Denver , at the eastern edge of the Rockies and the biggest city for six hundred miles. Outside Denver, the northern half of the state holds the most popular destinations, starting with the dynamic college town of Boulder and the spectacular Rocky Mountain National Park . The majority of the resorts that have made Colorado the continent's foremost skiing destination snuggle into the mountains to the west of Denver: Summit County attracts the most visitors, Vail is considered best for terrain, and Aspen boasts the glitziest après-ski scene. The far west of the state stretches onto the red-rock deserts of the Colorado Plateau. Pikes Peak towers over the enjoyable city of Colorado Springs , but the rest of the state's southeast quarter is mostly agricultural plains. To the southwest untouched old mining towns like Crested Butte and Durango stand in the mountains, while Mesa Verde National Park preserves perhaps the most impressive of all the cliff cities left by the ancient Ancestral Puebloan civilization.