As NASA's Curiosity rover roams Mars' surface, pushing man's frontier into space, the Census Bureau looks back at the American Frontier with its graphic representation of the population growth from the late 18^th to late 19^th century.  In 1790, the population extended up and down the eastern seaboard - from southern Maine deep into South Carolina - but the frontier remained close to the Atlantic Ocean.  

By the Louisiana Purchase in 1803, the frontier extended into the western portion of the U.S., and population centers on the East Coast expanded rapidly.  In the middle of the 19^th century, Americans pushed the limits of civilization well into the Midwest and established burgeoning cities throughout the region.  The frontier remained at borders drawn in the Louisiana Purchase, but the populace was well on its way to filling in the gaps from the East Coast to the Midwest.  When the gold rush caught the attention of millions of Americans, the frontier finally reached the West Coast, and people across the nation tried their luck in the gold-rich rivers of California. Moving onto the late 19^thcentury, the population’s reach extended throughout the entire continental U.S., and though gaps remained in the Midwest, the Superintendent of the Census declared the frontier to be nonexistent.