Gaia GPS app.
With the premium version you have access to every National Geographic Trails illustrated map including the national parks. Plus hundreds of other maps. It and CalTopo are arguably the gold standard in mapping apps/software although Gaia GPS is much more user friendly. CalTopo is better if you want to get super in-depth into making your own maps and things like that but it takes time to learn. Gaia GPS has most anything you could want for maps already available.