Beginning with small bands of nomadic hunter-gatherers, Native Americans have inhabited the Colorado River basin for at least 8,000 years. Between 2,000 and 1,000 years ago, the watershed was home to large agricultural civilizations—considered some of the most sophisticated indigenous North American cultures—which eventually declined due to a combination of severe drought and poor land use practices. Most native peoples that inhabit the region today are descended from other groups that settled there beginning about 1,000 years ago. Europeans first entered the Colorado Basin in the 16th century, when explorers from Spain began mapping and claiming the area, which became part of Mexico upon its independence in 1821. Early contact between Europeans and Native Americans was generally limited to the fur trade in the headwaters and sporadic trade interactions along the lower river. After most of the Colorado River basin became part of the U. S. in 1846, much of the river's course was still the subject of myths and speculation. Several expeditions charted the Colorado in the mid-19th century—one of which, led by John Wesley Powell, was the first to run the rapids of the Grand Canyon. American explorers collected valuable information that was later used to develop the river for navigation and water supply. Large-scale settlement of the lower basin began in the mid- to late-19th century, with steamboats providing transportation from the Gulf of California to landings along the river that linked to wagon roads to the interior. Starting in the 1860s, gold and silver strikes drew prospectors to parts of the upper Colorado River basin.