I'm confused. Once I upgraded my MBP-retina to Mavericks, I found that I had *two* "US Holidays" calendars -- one that I subscribed to, and another that apparently resided "On My Mac". I was able to delete the latter.
However, on my iPhone 5S running iOS 7.1, I have *two* "Us Holidays" calendars, to both of which I am subscribed, and I am unable to delete *either* (there's no delete button).
OK, so now I see what I had to do: Mavericks doesn't include an Apple-generated "US Holidays", correct? So I had to store the one I had manually subscribed to on "On My Mac" (and not on iCloud) so that it wouldn't be synched to my phone. For some reason, even that one couldn't be deleted from my iPhone.
It looks like subscribed calendars that are stored on iCloud are not deletable from one's iPhone; the only solution is to remove it from iCloud on your Mac.