RIVERSIDE, Calif. -

A woman threatening to pull a gun on a cashier robbed a department store in Riverside today, fleeing just before police arrived.

The robbery happened at 10:01 a.m. at a Nordstrom outlet in the Galleria at Tyler Mall, located just off the Riverside (91) Freeway on Tyler Street.

``A woman in a cowboy hat approached a customer service clerk on the third floor and passed her a note, saying she had a gun and wanted money,'' Riverside police Officer Bryan Galbreath told City News Service. ``She made gestures to her purse leading the clerk to believe the gun was present, though nothing was seen.''

The frightened store employee handed over an undisclosed amount of cash from the register, and the robber fled out of a side exit, Galbreath said.

Riverside police officers swarmed the location after receiving a 911 call, but the suspect was nowhere to be found.

The store was locked down for 30 minutes while officers conducted a search of the grounds. According to Galbreath, contrary to reports, no customers were forced to remain inside the store. However, several employees chose to lock themselves in backrooms until officers appeared.

No one was injured.

The suspect was described as black, around 50 years old with short hair, average height and heavyset. She was wearing glasses, a Nike T-shirt and blue jeans, carrying a brown purse.

Galbreath said surveillance video did not show her wearing the cowboy hat when she exited the store.

Anyone with information was urged to call the Riverside Police Department at (951) 826-5700.