OrganicMaps, all the trails I've been to so far in the US are available for offline navigation. No need to precache via gmaps and pray it won't get deleted
Edit: OpenStreetMap which powers this is what AllTrails uses, but I'm not sure if they contribute back or not
I've just arrived in Norway (literally waiting as passport control) at the start of a three-week hiking-heavy Interrailing trip around Scandinavia and Central Europe. You better believe that I've got all of Europe downloaded in Organic Maps. Also, Organic Maps is a client for OpenStreetMaps which, for detailed foot-level maps, beats Google/Apple hands down and is, of course, open source.