What do the letters like CS, WR, TR, etc. on the maps mean?

Waypoint abbreviations are explained in this blog post.

I want to make a donation to Halfmile’s PCT maps but I can’t find the donate button.

We have decided to stop accepting monetary donations from hikers, but it would make us really happy if you made a donation to the Pacific Crest Trail Association. We know most of you are already PCTA members, so just send them a little something extra and tell them Halfmile sent you. You can use this handy donate page.

I’m having problems opening Halfmile’s printable PDF map files. When try to open the .ZIP file in Adobe Reader it comes up with an error saying it is invalid.

.ZIP files need to be uncompressed (expanded) before they can be opened with Adobe Reader. Windows users can find more information here. Macintosh users can find more information here.

How do the UTM coordinates used on Halfmile’s maps work?

See the excellent Quick Guide to Using UTM Coordinates or Using the UTM/MGRS map coordinate system from Maptools.com.