This may be due to Google Calendar. The only reliable way I have found to control what calendars get sync'd to iDevices, is a fairly hidden control panel on Google Calendar:
https://www.google.com/calendar/syncselect
This panel allows you to select which calendars will sync to your iDevice and iCal. Simply uncheck those you don't want in iCal or iPhone, and they will disappear from those devices, but remain in your Google Calendar list.
If you want to know more about these Calendars, you should visit the Google Calendar site. Then select 'Settings' from the Gear icon on the right, choose the "Calendars" tab, and then view the calendars listed. For example, if you have Google+, Google 'helpfully' creates a Birthdays calendar from your Circles. Some calendars you can delete by hitting the 'unsubscribe' link, but others, including the Google+ Birthdays calendar, you can not delete (thanks Google). However, the sync link above will prevent them from showing on your Apple Device.