Depends on the location, and how willing the people that KNOW where the trails are to share their knowledge with the rest of us. Where are you referring to, specifically ?
Southern California. I know where the trails are. I am looking for a map that is more detailed, has forest service trail numbers etc
I think the best forest service maps these days are the Travel Management MVUMs. These show ALL the roads and trails in a ranger district that are actually open. You have to search for them by forest and ranger district. Most of these are just pdf files, but slowly versions suitable for downloading to GPS devices are becoming available. But I have no notion of what format one needs for Locus.
I use Google Hybrid maps. This combines aerial and road info. It shows you Forest Service numbers etc.
Another Locus user here. Anyone have an update to this thread and possibly where to download MVUM-only maps for Locus?
I've found that Google gets the numbers wrong pretty frequently and shows roads that have been decommissioned, at least in the Olympic NF.