If you are planning to visit the parks in the US, National Parks iOS app is a good guide from National Geographic. It is available for iPhone only, but you can see it in iPad also. For Android users, there is Chimani app for Parks information.
The first guide is free it seems after that for more parks information you have to pay $1.99 in-app purchase.
"National Geographic presents a new, beautiful, and interactive guide to the national parks with a new app for iPhone. Whether you are seeking inspiration and planning your next trip or you’re looking for the ultimate in utility, National Geographic has everything you need to explore the U.S. national parks at your fingertips. Watch for updates as we continue to add more parks.
- Global and interactive map views with filtering by activity and seasonality- Personalized user space to track your favorite parks, activities, itineraries, photos, and more- Thousands of points of interest, all tagged with GPS coordinates for easy planning and locating- The top must-sees and must-dos for each park, curated by National Geographic editors- Stunning photo galleries for each park, plus rare vintage images from the National Geographic Archive- Photo tips from National Geographic photographers- Sharing through Facebook, email, and Twitter- Collectible park stamps- And much, much more!"You can download it from iTunes link.
