iCal is a wonderful calendar application that allows you to create and manage multiple calendars at a time. One of its strongest features is its capabilities to both share calendars over the internet and subscribe to calendars in a similar fashion.
The latter feature also allows you to add Holidays to our calendars. To do this, navigate in Safari or the web browser of your choice to http://www.google.com/calendar/.
Create an account if needed and enter into the Search field ‘US Holidays’ or any group of national holidays that apply to you and click the Search Public Calendars button.
Now, add one of the calendars. Once the calendar has appeared under “My Calendars” and on your Google Calendars, click on the drop down arrow next to the calendar and select Calendar Settings.
Find the iCal button on the Calendar Address row and click it to find a link that iCal knows how to handle. Clicking the link will launch iCal and ask you which Calendar you’d like to include it in.
I personally created a new Holidays calendar but it should work seamlessly with any of the calendars you’ve already added. Congrats! Your newly added Holidays should now appear in iCal.