There is a nice PDF map “project” for running trails, hiking trails, and mountain bike trails, as well as climbing locations, and back country powder. All the apps have the “project” suffix as they are crowd sourced via Adventure Projects.
The app is easy to use, and works with no cell service as long as the PDF maps are loaded. The only drawback is that they don’t have “every” trail, but slowly it seems their database is growing as the crowd contributes to the maps.
From the Trail Run Project website:
Is this really all free?
Yes, everything is completely free. We have no plans to charge for access to detailed data, maps, GPX downloads, or the mobile apps.
The app helped me a great deal in a few remote adventure areas. My first experience was a few years ago.