Mile markers, or mileposts as they are also known, are the vertical green signs on the edge of highways placed at one-mile intervals. Mile marker numbering begins at the most southerly or westerly point in a state. For example, if you enter Colorado from New Mexico, mile markers will increase as you travel north through Colorado. Likewise if you were to enter Colorado from Utah, mile markers would increase as you travel east through Colorado. California is the only state that does not use mile markers. Instead they use a Post Mile system with numbering beginning and ending at county lines.
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