SACRAMENTO, Calif.—The identity of the person whose Mega Millions ticket is worth half the $648 million jackpot remained a mystery Friday, but lottery officials said it's not unusual for big winners to delay claiming the prize while they seek advice about their new fortune.

One of two winning tickets for Tuesday's drawing was sold at a San Jose gift shop. The other was sold in Georgia and the winner already has been identified.

California Lottery spokesman Alex Traverso said the second winner has a year to claim the money.

"It's fairly common in cases like this that they've hired financial representation and an attorney so they come forward with a plan of action," Traverso said.

The jackpot comes to a total of $324 million per winner. If the person takes a lump sum, it's about $120 million after taxes.

"That's not a check you can just walk to the local credit union and plug into the ATM," Traverso said.

Of course, it's also common for people to have misplaced the ticket or simply have forgotten about it. If months go by with no claimant, Traverso said officials will identify the time the ticket was purchased and use surveillance cameras to try and get an image that can be released publicly.

Lottery officials say they have a pretty good record of tracking people down.

In one case in Bakersfield, a winner had forgotten about a ticket that was worth $23 million dollars. Traverso said the person saw their picture in the local paper, and remembered they'd left the winning ticket in the door pocket of their car.

The ticket had been set to expire in three weeks.

"That person came right in and claimed their $23 million," Traverso said.