Answer:
Confirmation bias
Step-by-step explanation:
Confirmation bias is the tendency to interpret information in a way that confirms one's preexisting beliefs. This type of bias prevents people from looking objectively at given situations and paves way to many false beliefs and stereotypes.
Stefanie sees a blond-haired, tanned guy walking around campus and she assumes he must be from California based on the way he looks. She assumes that everybody looking that way must be from California because she heard that belief so many times that she started believing it, without any proven evidence supporting this statement.