When I upgraded to Mavericks from Snow Leopard, my iCal calendar settings seemed to migrate poorly to Mavericks and ended up duplicating my Google Calendar. Two exact replicas and both would appear in Calendar->Preferences. However, when hitting the "-", it brought me to Internet Accounts and only one Google account was signed in. Removing my Google account from Internet Accounts only removed one of the calendars and I still couldn't remove the other stubborn calendar.
Found the solution here:
http://apple.stackexchange.com/questions/96185/cant-delete-calendars
Basically reset all your calendar settings by deleting everything (might want to backup everything first). Singing into Google with Mavericks' Internet Accounts seemed to do the trick.
Home > Library > Caches > com.apple.ical
Home > Library > Calendars > Calendar Cache, Cache, Cache 1, 2, 3, etc. (Do not remove Sync Cache or Theme Cache if present)
Home > Library > Preferences > com.apple.ical (There may be more than one of these. Remove them all.)
YMMV
