To anyone visiting Cotabato City today, it seems puzzling that this capital town has witnessed more history than any place in Mindanao. In the hydrograph of the island, the Pulangui or Rio Grande de Mindanao in Spanish accounts stands out as a landmark. Cotabato City lies, just eight nautical miles above the Pulangui mouth. The land area of this ancient capital virtually is seated on deltaic deposits.
As in centuries past the center of the population now is situated along the left bank of the northern branch of the Pulangui River. At the foot of the hill in this site lies a stone fort, from which the city derived its name, kuta being maginadanao word for “fort” and wato for stone. For defensive reasons the hill has also served as a natural lookout. Hence, it acquired its native name tantawan. But etymologically, these entire magindanao names place are hispanized or agelicanized into Cotabato.
Most of the part of Cotabato City is at an elevation only slightly above sea level. The presence of elevated Pleistocene coral reefs, as in the vicinity of Fort Tantawan, Timako Hill, indicates that the area southwest of a line from the mouth of Pulangui River to Sarangani Bay was once separated by water from the rest of mainland Mindanao. Coral limestone has also been found in several places in the hills, a short distance north of Sarangani Bay, in what is now General Santos City. Thus, geologically, scholars maintain that recent uplifts raised the shallow channel above sea level, and rivers began to deposit their sediment during the glacial epoch. The city’s location at the mouth of the pulangui river basin has made receiving end of considerable quantities of silt raised the plains of Cotabato some 500,000 years ago.
At the present moment of its geophysical formation, the city of Cotabato still accumulates a fairly large amount of soil a fairly large amount of soil deposits carried downriver by the runoff by the Cotabato Cordillera along the south western coast of Mindanao, and from the erosions of the mountain ranges which separate the Cotabato River Valley from the lake Region.