Editor’s note: Sign up for Unlocking the World, CNN Travel’s weekly newsletter . Get news about destinations, plus the latest in aviation, food and drink, and where to stay. CNN  —  Peak season in many US national parks has begun. Families heading outdoors during spring break are arriving by the carload to enjoy hiking, admire wildlife, learn about history and nature and enjoy all that the National Park system offers. When they arrive with their tents, hiking poles and sunscreen, they might