Trail Establishment and Maintanance Resources?

I know this is only tangentially related to hardware, but this seems like a place where people might know an answer.

Are there any good books/ youtube channels/ articles/ websites/ or organizations that could help me get a solid understanding of how hiking trails are formed and how to maintain them?

I have two situations where I'd like to do some work with trails... on is at a popular established local crag (East A near Durango) and the other is at a crag on forest service land that has no trails.

In the situation with the established area, there's a trail down a blank muddy face that is eroding badly.  I sure that there are probably 10-20 folks (or more) who have worked on this over the years and who have both opinions about what/how the trail should be maintained, so I don't want to step on their toes with out at least trying to inform myself.  I am planning to reach out to the local group and see when we might be able to go out and work, but before I do that I'd like to be more educated about some parts of that work.

With the unestablished area, I just want some guidance on where and how to establish some trails that don't suck; I feel like it's a worthwhile project and if other people climb there it would be very helpful for future climbers if we aren't all trying to scramble straight up a loose, 50° dirt slope above a cliff.

So, any thoughts, experiences or resources on those lines of inquiry would be helpful.

The MTB crowd has a fair amount of info on this.  Search IMBA and trail building.  I think there are also a fair number of resources out there.  Quick search turns up this (which I wish was around a while ago when I started looking)

https://trailism.com

AF will have resources as well.

This biggest things I learned is that bench cutting is KEY to trails surviving on slopes and is absolutely one of the most difficult, character building manual labor efforts you'll do outside.  

Check out the "Trail Construction and Maintenance Handbook". Its from the Forest Service. Avoid using water bars and other features that require maintenance, build grade dips instead. Each landowner has different rules and regulations for establishing new trails or trail maintenance. There are NEPA rules that limit the ability to reroute trails depending on who owns the property. If it's government property, a reroute is unlikely. It can take many years and cost a lot of money to get it approved. Is there a local climbing organization that already works on this area that may have a better understanding of trail construction and area needs?

I’ll second what Tom said - the FS handbook has some good diagrams and design tips. Link:

USFS Trail Construction and Maintenance Notebook

Thanks for the resources... these are exactly what I had hope to be shown.

Hey John, I have a copy of the book Appalachian Trail - Design, Maintenance, Construction published by the AT conservancy.  It’s not specific to the AT, but all good trailbuilding in general.  Im sure it would be useful for you.  I’m happy to send it to you if you cover the shipping.