We spend every other summer in the mountain west, mainly western Colorado. Some of the apps I enjoy are: The Audobon series, trees, insects, reptiles and wildflowers
Mapquest
National Parks by National Geographic - doesn't have them all but the ones they have are very well done.
Woodall's
RV Checklist
Truckster for diesel along with gas buddy
Oh Ranger - governmental campgrounds
Low Clearance by Allstays - handy when off the Interstate system
Weather Chanell, Weather Bug and Imap Weather Radio tracks your location for alerts to bad weather. Then I have a couple of Hurrican apps for here on the Gulf Coast.
Plus the ereader apps, Kindle and Audible for listening to books.
When in the west, away from light congestion of the cities, the App Night Sky is enjoyable as it points out what you can see from that location, when you are outside and look up.
These are some of the main ones I use when out west with our RV.