Good day trip from Fort Smith, Arkansas?

I am going to Fort Smith, AR for a week in March to work with Habitat for Humanity. I will be with a group of 12 and we have Sunday off. We would like to go somewhere that doesn’t cost very much and is in reasonable driving distance. We were thinking maybe heading to Tulsa or to the Ozark National Park for some hiking. Any suggestions?

http://www.arkansasstateparks.com/things-to-do/trails/park.aspx?id=4
hiking at Devil’s Den State Park might be fun