The woman robbed the Bank of the West in the 27000 block of McBean Parkway in Valencia. She passed a note to a teller demanding cash and threatened to detonate a bomb if the teller refused.
Witnesses described the woman as having a glamorous disguise, including a wig and large sunglasses. She was also seen casing other banks in the area during the day of the robbery.
The woman is between 20 and 25 years old, 5 feet 3 inches tall and about 125 pounds, authorities said.
Anyone with information should dial 911.