iCloud: Delete a calendar
When you delete a calendar from your Calendars list, all events associated with the calendar are also deleted.
You can’t delete all of the calendars in the list because it must always contain at least one calendar.
Delete a calendar
Click Edit below the sidebar.
Click the Delete button to the right of the calendar’s name, then click Delete.
If the calendar is shared, a window appears asking whether or not to send a notification email to calendar participants. If you choose not to notify participants via email, they’re notified the next time they sign in to iCloud that the calendar is no longer available.