Output from %timedatectl status is "Time zone: America/Denver (EDT, -0400)"
Something is corrupt since Denver is in fact MDT, -0600.
Is there a file I can remove and replace?
Edit: As Jaromanda has pointed out, the file to replace is "Navajo", which is pointed at by Denver. Deleted Navajo, copied over Edmonton and renamed it to Navajo. Now all is well when I select Denver as my timezone and reboot.
I'll attempt to mark this question as answered if this is possible. Or someone reading this with more experience, kindly feel free to do so.