A California collector has returned two 304-pound Civil War cannons - valued at more than $15,000 each - that were stolen from Highland Cemetery in August.

Police said Doug Howser of Lancaster, Calif., told them he did not know the antique Dahlgren Boat Howitzers had been stolen when he bought them from a Michigan man for $2,900.The 36-inch bronze cannons were manufactured in 1854 and were used on Union ships during the Civil War. They were mounted in a cement foundation in the veterans' memorial at the 30-acre cemetery in the late 1950s.

Police Chief John Simpson said the cannons were donated to the city by the William Noble Post of the Grand Army of the Republic, an organization of Civil War veterans that had btained them from the Navy.

Simpson said Howser called police and told them he had the cannons when he realized they had been stolen. A short time later, Howser sent the cannons back to Gladwin.

Police said two or more people took the cannons from the cemetery in early August. One suspect, who has been identified but not yet arrested, apparently picked up one of Howser's business cards at a Michigan gun show, telephoned Howser and offered to sell him the cannons, they said.