Officers say the woman, thought to be about 20-years old, walked into a pawn shop in the 19800 block of Highway 99 at about 1:30 p.m. on Saturday.
After loitering around the store for several minutes, the woman asked to see some jewelry in a display case. When the employee took out two trays full of rings, the woman grabbed them and ran out of the store.
Police believe another person was waiting for her outside in a car. Detectives are now working with other agencies to see if the same woman has robbed any other stores in the area.
Police say the thief is a black woman who stands roughly 5'2" tall and weighs about 160 pounds. She was wearing red shorts and a black shirt and Saturday.
Anyone with information about the woman is asked to call police.