(San Fran Twnshp, MN)  --  The State Fire Marshal's Office is investigating a morning fire (Tues) at a Carver County dairy farm that killed around 70 calves and 13 cows.  Belle Plaine Fire Chief Todd Otto says they were able to save about a dozen calves which are closely being watched due to exposure to smoke and heat.  Farm workers discovered the building engulfed in flames when they arrived to milk the cows.  The owners are on vacation.  Otto says the preliminary cause is electrical.  Damage estimates are between 100- and 200-thousand dollars.