The first people to reach North America almost certainly did so without knowing they had crossed into a new continent. They probably would have been following game & agreeable weather, as their ancestors had for thousands of years, possibly along the Siberian coast & then across the land bridge. Genetics studies have shown that the indigenous inhabitants of the Americas are descended from a group that diverged from its Siberian ancestors beginning sometime around 23,000 years before present & remained isolated in Beringia (the region of land that once connected Siberia & North America) for an extended period of time. When the glaciers covering North America melted enough to make the Pacific coast navigable, southward travel became possible, & patterned genetic diversity across North & South America reflects these early movements.
Once in Alaska, it would take these first North Americans thousands of years more to work their way through the openings in great glaciers south to what is now the United States. Evidence of early life in North America continues to be found. Little of it, however, can be reliably dated before 12,000 B.C.; a recent discovery of a hunting lookout in northern Alaska, for example, may date from almost that time. So too may the finely crafted spear points & items found near Clovis, New Mexico.
Similar artifacts have been found at sites throughout North & South America, indicating that life was probably already well established in much of the Western Hemisphere by some time prior to 10,000 B.C.
Around that time the mammoth began to die out & the bison took its place as a principal source of food & hides for these early North Americans. Over time, as more & more species of large game vanished — whether from overhunting or natural causes — plants, berries, & seeds became an increasingly important part of the early American diet. Gradually, foraging & the first attempts at primitive agriculture appeared. Native Americans in what is now central Mexico led the way, cultivating corn, squash, & beans, perhaps as early as 8,000 B.C. Slowly, this knowledge spread northward.
By 3,000 B.C., a primitive type of corn was being grown in the river valleys of New Mexico & Arizona. Then the first signs of irrigation began to appear, and, by 300 B.C., signs of early village life.
By the first centuries A.D., the Hohokam were living in settlements near what is now Phoenix, Arizona, where they built ball courts & pyramid-like mounds reminiscent of those found in Mexico, as well as a canal & irrigation system.
