Remove one end from each of the three 1-pound cans; rinse cans, dry, and grease well.
In a large bowl, stir together graham flour, all-purpose flour, soda, and salt until thoroughly blended.
Stir in yogurt, molasses, raisins, and walnuts; mix well.
Divide batter evenly into cans.
Bake in a 350° oven for about 1 hour or until a wooden skewer inserted in center comes out clean.
Cool in cans for about 10 minutes; then turn out and stand loaves upright on a rack to cool completely.