Gaia and Natural Atlas still let you do a bunch for free

Topo Nonad on iPhone. The interface allows for easy access to USGS maps. I know those are public domain; you’re only paying for the ease of access. And it’s a “99 year subscription”. You pay one time and you have the app for 99 years rather than a monthly subscription. I think it’s like $20 now.

You can upload custom geospatial PDS as well. So if you use the CalTopo website and create a custom map you can download it and view it in the Topo Nomad app.

One of the neat features is that it also has historic maps. So if you find an old road or trail you can search really old maps to see if it’s marked. And Vice versa; you can find old roads on outdated maps that have long since been abandoned but are still there in some form.

I know of a few spots where trails were re-routed because of blowdowns or the trail collapsing into a ravine or obstacles. It’s nothing major; they’re all just a mile or so different. But those sections still exist.