As an avid hiker, I have found these apps invaluable as they help one navigate when no service is available.
Maverick: GPS Navigation
This app’s offline map support and compass guide you when you have no network access. It also has links to online maps.
AlpineQuest GPS Hiking
This app’s storage system to access online maps when you have no network access helps guide you where you need to travel on your hike.
BackCountry Nav Topo Maps GPS
This app allows one to use offline topo maps and aerial photography to navigate the trails.