I don't see United States holidays in my 2013 calendar. I tend to plan in advance, and would like to have the holidays in my calendar. I thought that would be automatic with ical, but am new to Mac. They were automatic with Outlook. Thanks!
You can download from Apple. Apple publishes one for the US and there are many others.
In Calendar, go to Help menu, then "Find Calendar Subscriptions..."
It is a little hard to find, but I sorted the available calendars by Alphabet and then found US Holiday Calendar on page 7.