When your characters are aiming to get from one far place to another, what better location to set it than the United States? (Okay, there are probably more, but Eagle Land stereotype demands that Americans only know about America.) It's big, it's very diverse in geography and culture, and there are plenty of landmarks on the way.
Although most of the time taking place in the United States, some parts of it might take place in Canada or Mexico. Stories about a journey across Canada or Mexico can also qualify.