Ellensburg, Washington is a real town and is where the movie was filmed. It is in central Washington.
At the mayoral announcement in the alternate universe, a woman with a geiger counter gets readings from the magic mirror, refers to it as a "nuclear artifact", and calls the main characters the "Hanford Smugglers". Hanford is an actual nuclear power plant located near Richland, Washington, which is located about 100 miles from Ellensburg, Washington.