In the early 1960 the construction of Ambuklao Dam displaced thousands of people living in the area. Those directly within the dam site were relocated; those whose dwellings were submerged by the rising dam water became literal refugees fleeing their habitation to move out to other places.
Sometime in 1966 a group of these refugees staggered into a thickly forested group of mountains that was to be the present Don Mariano. They were Moise Sepiacan, Walter Dupinos, Borsio Dioniso, Moreno Camates, Thomas Pascual, and Francisco Gambala. The group was a small mixture of Ibaloys and Kankanaeys. They settled in what was then called Gananat.
At that time two longing companies----the Bagabag Sawmil and the Mountain Sawmill --- started operations in the general direction of that area, hacking out wide paths to transport their logs. In many ways those paths were a blessing to the early settlers. The group of Sepiacan occupied the place where the Bagabag sawmill operated.
However, the settler were soon faced with great uncertainties when the longing concessionaires attempted to drive out the people from Campamento, Rafael Palma, Dumanisi, and Magsaysay on the pretext of making the whole area as a watershed reservation.
Bearing Documents of Displacement from the Ambuklao Da, the people sought the assistance of then Diffun Mayor Mariano Pimentel who in turn endorsed the matter to then Senator Leonardo Perez. The good (BFD), the government agency charged with managing the forests of the country and the implementation of forest policies.
The BFD granted the petition, and the people in the areas mentioned remained in their respective places.
Out of gratitude to the Mayor and Senator, when the settlement of the Ibaloys and the Kankanaey was recognized as a barangay was subdivided into 5 sitios --- Gananat Batumbaket, Duminatlo, Eden, and Longpond.