The mountains of Mindanao can be conveniently grouped into five ranges, including both complex structural mountains and volcanoes. The structural mountains on the extreme eastern and western portions of the island show broad exposures of Mesozoic rock with ultrabasic rocks at the surface in many places along the east coast. Surface rock in other areas of the island is mainly Tertiary and Quaternary volcanic or sedimentary.
Paralleling the east coast, from Bilas Point in Surigao del Norte to Cape Agustin in southeast Davao, is a range of complex mountains known in their northern portion as the Diwata Mountains. This range is low and rolling in its central portion. A proposed road connecting Bislig on the east coast with the Agusan River would pass through a ten-mile (16 km) broad saddle across the mountains at a maximum elevation of less than 250 meters, while the existing east-west road from Lianga, 30 miles (48 km) north of Bislig, reaches a maximum elevation of only 450 meters. The Diwata Mountains, north of these low points, are considerably higher and more rugged, reaching an elevation of 2,012 meters in Mount Hilonghilong, 17 miles (27 km) northeast of Butuan City. The southern portion of this east coast range is broader and even more rugged than the northern section. In eastern Davao, several peaks rise above 2,500 meters and one unnamed mountain rises to 2,810 meters.
The east-facing coastal regions of Davao and Surigao del Sur are marked by a series of small coastal lowlands separated from each other by rugged forelands which extend to the water’s edge. Offshore are numerous coral reefs and tiny islets. This remote and forbidding coast is made doubly difficult to access during the months from October to March by the heavy surf driven before the northeast trade winds. A few miles offshore is found the Mindanao or Philippine Deep. This ocean trench, reaching measured depths of 35,400 feet (10,800 m), marks one of the greatest depths known on the earth’s surface.
A second north-south range extends along the western borders of Agusan and Davao provinces from Camiguin Island in the north to Tinaca Point in the south. This range is mainly structural in origin, but it also contains at least three active volcano peaks. In the central and northern portions of this range, there are several peaks between 2,000 and 2,500 meters, and here the belt of mountains is about 30 miles (48 km) across. West of Davao City are two active volcanoes: Mount Talomo at 2,693 meters and Mount Apo at 2,954 meters. Mount Apo is the highest point in the Philippines and dominates the skyline. South of Mount Apo, this central mountain belt is somewhat lower than it is to the north, with peaks averaging only 1,100 to 1,800 meters.
In Western Mindanao, a range of complex structural mountains forms the long, hand-like Zamboanga Peninsula. These mountains, reaching heights of only 1,200 meters, are not as high as the other structural belts in Mindanao. In addition, there are several places in the Zamboanga Mountains where small inter-mountain basins have been created, with some potential for future agricultural development. The northeastern end of this range is marked by the twin peaks of the now extinct volcano, Mount Malindang, which rise splendidly behind Ozamis City to a height of 2,425 meters. Mount Dapia is the highest mountain in the Zamboanga Peninsula, reaching a height of 2,617 meters (8,586 ft). Meanwhile, Batorampon Point is the highest mountain of the southernmost end of the peninsula, reaching a height of only 1,335 meters (4,380 ft); it is located in the boundary of Zamboanga City.
A series of volcanic mountains is found near Lake Lanao in a broad arc through Lanao del Sur, northern Cotabato and western Bukidnon provinces. At least six of the twenty odd peaks in this area are active and several are very impressive as they stand in semi-isolation. The Butig Peaks, with their four crater lakes, are easily seen from Cotabato. Mount Ragang, an active volcano cone reaching 2,815 meters, is the most isolated, while the greatest height is reached by Mount Kitanglad at 2,896 meters.
In southwestern Cotabato, still another range of volcanic mountains is found, this time paralleling the coast. These mountains have a maximum extent of 110 miles (180 km) from northwest to southeast and measure some 30 miles (48 km) across. One of the well-known mountains here is Mount Parker, whose almost circular crater lake measures a mile and a quarter in diameter and lies 300 meters below its 2,040-meter summit. Mount Matutum is a protected area and is considered as one of the major landmarks of South Cotabato Province.
A second important physiographic division of Mindanao is the series of upland plateaus in Bukidnon and Lanao del Sur provinces. These plateaus are rather extensive and almost surround several volcanoes in this area. The plateaus are made up of basaltic lava flows interbedded with ash and volcanic tuff. Near their edges, the plateaus are cut by deep canyons, and at several points spectacular waterfalls drop to the narrow coastal plain. These falls hold considerable promise for development of hydroelectric energy. Indeed, one such site at Maria Cristina Falls has already become a major producer. Because the rolling plateaus lie at an elevation averaging 700 meters above sea level, they offer relief from the often oppressive heat of the coastal lowlands. Lake Lanao occupies the major portion of one such plateau in Lanao del Sur. This largest lake on Mindanao and second in the country is roughly triangular in shape with an 18-mile (29 km)-long base. Having a surface at 780 meters above sea level, and being rimmed on the east, south and west by series of peaks reaching 2,300 meters, the lake provides a scenic grandeur and pleasant temperature seldom equaled in the country. Marawi City, at the northern tip of the lake, is bisected by the Agus River, which feeds the Maria Cristina Falls.
Another of Mindanao’s spectacular waterfall sites is located in Malabang, 15 miles (24 km) south of Lake Lanao. Here the Jose Abad Santos Falls present one of the nation’s scenic wonders at the gateway to a 200-hectare national park development.
The Limunsudan Falls, with an approximate height of 800 ft (240 m), is the highest waterfalls in the Philippines; it is located at Iligan City.