50,000: Number of years ago that some scientists believe humans first lived in what is now North America

Circa 1000: Year Leif Eriksson, sailing west from Norway to Greenland, lost his way and came upon North America

1497: Giovanni Caboto, AKA John Cabot, arrived on the North American mainland

1498: Cristoforo Colombo reached the North American mainland for the first time, on his third voyage

1869: Year Columbus Day was first celebrated by Italians in San Francisco

Source: Various Web sites