It is considered as the center of rice production in the province of Samar, and known for its "Mayao-Mayao Festival" which is celebrated annually. Barangay Poblacion Mambog is the seat of government, and the economic, cultural, educational, trade and industry center. It lies at the southwest central coast of Samar Island and crossed along by the Pan-Philippine Highway (Daang Maharlika/National Road).
Pinabacdao was established in 1749 but became a barrio in 1902 as part of the Municipality of Calbiga. It was then reestablished by Executive Order No. 02 series of 1946 issued by President Manuel A. Roxas, and separated from Calbiga as a reestablished municipality on July 16, 1946.