Preheat oven to 350°F Grease a 9 inch square cake pan.
Peel and cut orange into pieces; remove seeds. Combine orange, banana and raisins in food processor and chop coarsely. Combine flour, baking soda, cinnamon and salt.
Cream together margarine, sugar and eggs in large bowl on high speed of electric mixer until light and creamy. Add fruit mixture. Add dry ingredients alternately with buttermilk and vanilla, mixing lightly after each addition. Spread batter evenly in prepared pan.
Bake for 50 to 55 minutes or until toothpick inserted in center comes out clean.