Some Wisconsin quarters issued last year are turning out to be worth considerably more than 25 cents.

Coin collectors say quarters with two variations in the design of a cornstalk on the back of the coin have been spotted at Tucson, Ariz., and San Antonio, Texas.

Rick Snow, who owns Eagle Eye Rare Coins Inc. (search) in Tucson, said he started paying $50 each for the quarters when he learned of them.

"As soon as word got out about that, the prices escalated," Snow said.

On Monday, he was offering a set of three Wisconsin quarters — the normal one, one with a leaf marking pointed up and a third with the marking pointed down — for as much as $1,099. Individual coins with the variations were selling for $500 to $600, depending on condition, he said.

The U.S. Mint (search), which produced 453 million Wisconsin quarters for its state coin series, is trying to determine how the differences came about.

"Throughout history, there have been some instances of variations — very, very rare instances," said U.S. Mint spokesman Mike White. "If there is any kind of situation like this, we just take a very close look at the process and all the different steps."