While much of the campaign has been going on along the Atlantic coast (New Hampshire, Virginia, North Carolina, and Florida) and in the Midwest (Wisconsin, Iowa, and Ohio), the West has been somewhat neglected. Nominally, there are three Western swing states: New Mexico, Nevada, and Colorado, but New Mexico has become so blue that it is really off the table now. Of the others, Colorado is the bigger prize (9 EVs) but Nevada (6 EVs) is also worth having. To emphasize that he hasn't written off the West, right after the third presidential debate Mitt Romney flew to Nevada for a rally, then went on to Colorado for another one, at the Red Rocks Amphitheater, where he spoke to an estimated 12,000 fired up supporters.
Neither candidate regards Colorado as a "must win" state, in the sense of Ohio or even Virginia, but if Romney wins Florida, North Carolina, and Virginia, Colorado will become crucial. If this scenario prevails, the election results won't be known until late in the evening at best, because Colorado is on Mountain Time.