Moses Solis, 20, of Rialto, was arrested without incident Monday night on the 200 block of Base Line Road.
He's facing several charges, including aggravated sexual assault of a child.
Surveillance video taken on Sunday inside one of the stores at the mall shows a man entering the women's restroom.
Investigators said Solis assaulted the girl after following her inside the restroom.
It's unknown if there are other victims. The incident remains under investigation.
Anyone with information was asked to call investigators at (951) 247-8700.