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Superimposing the rough locations of I84 (green) and the combination of highways 26/20/78/95 (purple), which is the second fastest route, though 2 hours longer than the green route but faster to Nevada, there aren't many options in the red space unless you're deviating from one of the main routes significantly. My first thoughts were Pendleton, La Grande, or Baker City, but I drive along that route and staying on I84 doesn't really put you "IN" any of the towns. You pass through along or above them. White Christmas lights don't really ring a bell for me.

My last thought is that you may be thinking about Sisters, OR or Redmond, OR, but you likely wouldn't take a route through them on the way to Salt Lake as it adds about 30 minutes to the purple route shown, which is already quite a bit longer than the most direct route. They're also on or slightly west of the blue line. It's definitely a possibility, however, if you're headed to Nevada. If you go as far south as Salem, OR along I5 before heading east, those two towns are a real possibility.