Boulder and Denver have cold, but it's mild enough that it can be dealt with somewhat using coats, blankets, sleeping bags, and tents. It doesn't have heat in the summers like New York City or Chicago do, or most of the year like Atlanta, Houston, and Miami do. 20 degrees below room temperature is much easier to handle than 20 degrees above room temperature, because there isn't anything wearable that protects people from heat like coats protect people from cold.