(This is a exert from http://chimac.net/)
1. “On your iPad, go to Settings > Mail, Contacts, Calendars.
Under Accounts, tap Add Account
Tap Other, and under Calendars, tap Add Subscribed Calendar
In the Server box, type http://ical.mac.com/ical/US32Holidays.ics
Tap the next button, and when the subscription box appears, tap the save button. No other entries are required.
Open the Calendar app and tap the Calendars button at the top left. You’ll find your new holiday calendar at the bottom of the list under “Subscribed”.
To unsubscribe, go back to Settings > Mail, Contacts, Calendars. Tap US Holidays Calendar under Accounts, tap the red “delete account” and tap “Delete”.”