My historian is Frederick Jackson Turner who is known for his study and research on the American Frontier. He considers pioneers of the west distinctly American and believes it is because of them and not Puritan Colonists or slave holding Southerners that American culture was developed. All of the readings I have done so far (for the wiki) suggest that it is because of Turner that the fascination with the frontier and American image exists.
The link provided is to a BBC video. The video demonstrates the American public’s interest and self-identification through the history of the frontier, the American West. Much of what Turner wrote (though later rejected as too general a view) still influences the way in which Americans think of their past as unique and distinct.