The large Abra and Mestizo rivers, together with the rivers of Bantay, Bantaoay, Nauman and Santo Tomas serve as part of a network that drain the Vigan plains. These rivers are not only important in safekeeping the city from floods, they also served as important ways of transport for trade-related activities from the 15th century to the 19th century, that helped make Vigan a thriving center. The most vital of these rivers is said to be the Mestizo River which was used by the small vessels to transport goods and people.
There is a faulting trend in the Vigan plain that ends in Santa Catalina.