From the site’s description:

A Contra Dance is also known as an Oldtime Country Dance or a Barn Dance or any number of names that have been given to it over the years in different areas and cultures of the U.S. It has also been around since the 17th century. The dances are called by a caller with a short instruction before each dance. During the evening besides Contra there may also be traditional squares, Irish Ceili, English Country Dances, Polkas and waltzes. Contra Dancers always dance to live music and at our dance the music is provided by the Sonora Contra Dance Players including banjos, fiddles, flutes, penny whistles, guitars, mandolins, autoharps and any other instruments that show up to play Oldtime and Celtic music.

Sonora Contra Dance Site
http://squaredancer8.wordpress.com/welcome-to-the-sonora-contra-dance-site-2/