Mervyns Department store is once again open and customers are being allowed inside after the store was evacuated this morning.
Fire fighters were dispatched to the scene at about 9:45 in response to reports of smoke in the building.
Sonora Fire Chief Mike Barrows says fire crews thoroughly examined the building but were unable to locate the source of the smoke.
Barrows says the building´s heating and air conditioning units were also checked and found to be working properly.
The smoke was initially discovered in the shipping and receiving section in the rear of the store. Fire crews left after it was determined that the smoke had stopped.
Barrows says investigators are on-scene, but the cause of the smoke may never be known.