This recipe is from an old newspaper clipping, no date. The picture on the back looks like this could be from the 1970s.

Cocoa Cola Sheet Cake

2 cups all-purpose flour
2 cups sugar
1/2 pound margarine
2 teaspoons cocoa
1 cup cola beverage
1 1/2 cups miniature marshmallows
1/2 cup buttermilk
1 teaspoon soda
1 teaspoon vanilla
2 eggs

Icing:
1/4 pound margarine
2 tablespoons cola beverage
3 teaspoons cocoa
1 pound confectioners sugar
1 cup chopped nuts

Combine margarine, cocoa, cola beverage and marshmallows in top of a double boiler. Heat over boiling water until marshmallows melt and mixture comes to a boil. Add to dry ingredients; beat 2 minutes. Add all remaining ingredients. Mix well. Bake in a greased 12x15x1-inch sheet cake pan at 350° for 40 minutes or until cake tests done. Meanwhile, prepare ICING: combine margarine, cola and cocoa in a medium saucepan. Bring to a boil over medium heat and cook 5 minutes. Remove from heat and blend in confectioners sugar and nuts. While still hot, pour over hot cake.