Geographical Profile

Land Area, Location and Boundaries

GAMU is the oldest municipality in the Mallig Plains.  It is located on the central portion of the province of Isabela.  It is approximately 10 kilometers away from the Provincial Capitol of Isabela, 101 kilometers to the Regional Center at Tuguegarao City, Cagayan and about 395 kilometers from the National Capital, the City of Manila.

The municipality is bounded on the north by the Municipality of Ilagan, the capital town of Isabela, on the southeast by the Municipality of Naguilian, on the south by the Municipality of Reina Mercedes; on the southwest by the municipality of Burgos; and on the northwest by the Municipality of Quirino.  The municipal center of Gamu is situated at approximately 17° 3′ North, 121° 50′ East, in the island of Luzon. Elevation at these coordinates is estimated at 51.9 meters or 170.2 feet above mean sea level.

Gamu has a total land area of 12,860 hectares.  It ranks as the 22th largest municipality out of 34 municipalities and 2 cities of the province.


Based on the great-circle distance (the shortest distance between two points over the surface of the Earth), the cities closest to Gamu are Ilagan, Cauayan, Santiago, Tabuk, Tuguegarao, and Candon. The nearest municipalities are Naguilian, Reina Mercedes, Luna, Quirino, Burgos, and Benito Soliven. Its distance from the national capital is 286.80 kilometers (178.21 miles). The following list delineates such distance measurements.

 Nearest towns:

Naguilian, Isabela, 2.67 kilometers (1.66 miles) to the South (S4°E)

Reina Mercedes, Isabela, 6.93 kilometers (4.30 miles) to the South (S8°W)

Luna, Isabela, 14.10 kilometers (8.76 miles) to the Southwest (S52°W)

Quirino, Isabela, 14.34 kilometers (8.91 miles) to the Northwest (N46°W)

Burgos, Isabela, 15.04 kilometers (9.34 miles) to the West (N81°W)

Benito Soliven, Isabela, 15.30 kilometers (9.51 miles) to the East‑Southeast 

 Nearest cities:

Ilagan, Isabela, 46.13 kilometers (28.66 miles) to the Southwest (S54°W)

Tuguegarao, Cagayan, 59.25 kilometers (36.82 miles) to the WestNorthwest (N65°W)

Cauayan, Isabela, 71.21 kilometers (44.25 miles) to the Southwest (S45°W)

Tabuk, Kalinga, 84.60 kilometers (52.57 miles) to the West (N88°W)

Santiago, Isabela, 107.29 kilometers (66.66 miles) to the Southwest (S44°W)

Candon, Ilocos Sur, 191.85 kilometers (119.21 miles) to the West (S84°W)

 Distance from Manila: 337.78 kilometers (209.89 miles) to the SouthSouthwest (S24°W)

Soil Type

Based on the data supplies by the Bureau of Soils, the Municipality of Gamu has five (5) types of soil.


This type of soil is found in the barangays of   Guibang, Songsong, Upi, Buenavista, Lenzon and the entire Poblacion.  The loam type is similar to those of the sandy loam series.  However, the former has much finer texture and thus many of its physical properties are relatively more intense than those of the latter.  For instance, the water holding capacity of San Manuel loam is greater, its water weighing more than half of its weight.  In other words,  San Manuel Loam is not droughty as San Manuel sandy loam.  The principal crops grown on this type of soil are corn, tobacco and legumes.

San Manuel Loam occupies an area of 6,211.2 hectares or a 48% share of the municipal land area.


These types of soil are dark gray to grayish in surface and have plenty of iron characteristics, which appear as rock outcrops.  The cultivated areas are devoted to lowland rice, corn and tobacco.  A large area is covered with native areas, which is utilized for pasture.

Cauayan sandy loam needs fertilization and application of lime.  Soil exhaustion is very evident in many cornfields.

The total area occupied by this soil type is 3,493.8 hectares representing 27% of the land area of Gamu.


Bago Clay Loam is the third most prevalent soil type occupying 2,717 hectares or a 21% share of the total land area of Gamu.  These are alluvial soils characterized by the abundance of iron concretions on its surface which coalesce to form larger ones.

The soil type is usually planted with rice during the rainy season.


An area of 415.4 hectares is covered by Bago Sandy Loam.  This soil type represents 3.21% of the total land area of the municipality.  This soil type is characterized by a dense compact brown layer in the substratum which sometimes impede internal drainage.  It is usually planted to diversified crops like mungbean, tobacco, beans and vegetables.


Bago Sandy Clay Loam cover 102.2 hectares comprising .79% of the municipality’s total land area.  Diversified crops thrive best in this soil type.


The climate of Gamu falls under the type III characterized by no pronounced season.  Generally, the climate is regularly mild, warm during the dry season and cool during the wet season.  The rainy season starts in September and lasts up to January although the month of May brings in its thunderstorms.


The rainfall of the municipality is to some degree influenced by its topography or orographic barriers.  The eastern portion of the municipality with higher ground elevations and affected by the presence of Sierra Madre Ranges on the east and a cooler air can cause greater condensation of water vapor which in turn produces more rains in the higher elevation on the east than in the plains of the municipality.  Hence, the municipality has two (2) types of climate.  The central portions with elevations ranging from less than 100 – 300 experience intermediate rainfall while the western tip whose elevation is less than 100 is relatively dry the whole year round.


The hottest months of the year for Gamu are the months of May and June with 31 degrees Centigrade.  The month of January recorded the lowest temperature of 24 degrees centigrade.  The rest of the year enjoys a relatively warm and hot weather with temperature generally ranging from 26 – 30 degrees Centigrade.


Based from PAGASA, there are on the average twenty one cyclonic disturbances that affect the Philippine Areas of Responsibility every year.  Cyclones may either be typhoons, storms or depressions.

The frequency of occurrence of tropical cyclones over the Philippine Archipelago is not evenly distributed.  Most of occurrence of tropical cyclones hit the northern half of the country.  Only 10-20% or an average of 2-4 cyclones cross the Visayas and less than 10% or 2 cyclones pass through Mindanao.

The Province of Isabela in which Gamu is located is among the areas frequently visited by tropical cyclones.  During the period 1980-1996, 33 storms passed over the province or an average of two cyclones per year.


The municipality of Gamu as a generally flat to rolling terrain.  6,599.4 hectares or 51% of the total land area of the municipal area is plain.  Gently rolling to undulating in one general direction areas cover 3,493.8 hectares or 27% of the total land area and the rest accounting for 2,8846.8 hectares of 22% of the total land area is undulating to rolling in many directions.  The rolling areas are used partly of pastureland, orchard and other similar agricultural land uses.


The Cagayan River, Magat River, the Siffu River and the numerous tributary creeks form the natural drainage of the municipality.  The Cagayan River traces the southern and south central portion of the municipality.  The Siffu River runs along the entire northwestern portion while the Magat River is the natural boundary between Gamu and the municipality of Reina Mercedes.

These water bodies are a rich source of aquatic resources and are abundant of fishers for human consumption.

While these rivers provide additional source of revenue for the municipal government, they also pose grave threat to lives of the people and the properties of the residents situated along the riverbanks.  For the past years, thousands of hectares of land have been washed away by rivers whenever flood occurs.  For this reason, the people residing along the riverbanks look eagerly towards the construction of a flood control as the only salvation from floods.


Research conducted showed that the municipality has no fault zones.  Its bedrock foundations are those classified as either Recent Alluvium or Unconsolidated Sandstone.

Recent Alluvium are found on the areas surrounding and along the Cagayan River.  Underneath this Bedrock foundation are Baton and Vigo formations of the Middle Epoch.

Along the boundary of Ilagan particularly on the north and northwestern portion of Gamu the bedrock foundation is Unconsolidated Sandstones which is 200-400 meters thick.  The duration of formation is also fassiferous of the tertiary zone.


The municipality has two (2) land classification, Alienable and disposable land and forest or timberland. Forest lands occupy a very minimal area of 274 hectares or 2% of the total land area. Alienable and disposable lands are 98% of the total municipal area.

The only forest area of Gamu are found in barangays Songsong and Guibang. All the rest of the barangays are under the A n D land category.


Land capability classes found within Gamu are as follows: Class A, Class Be and Class Bw.  Based on the Soil Survey of Isabela.  Soil type classified under land capability A are San Manuel loam and Cauayan Clay Loam.  These types of soil are suitable for intensive cultivation and all crops common in the area can be grown. The Bago Series fall under the B land capability classes.


The municipality experiences erosion of topsoil from varying erosion sources.  2,458 hectares representing 19% of the total land are vulnerable to water erosion.  These are the areas straddling along the banks of the Cagayan, Magat and Siffu Rivers.  Chemical deterioration as erosion source covers an area of 1,552.8 hectares of 12% of the total land area of Gamu.  1,035.2 hectares or 8% share of the land area is subject to physical deterioration.  7,893.4 hectares or 62% of the total land area are apparently free from physical


During the occurrence of typhoons that bring heavy rains into the municipality, the areas along the three main rivers of the municipality are flooded.  Low lying areas of Barangay Lenzon, Upi, District I, District II and District III are usually the victim of flooding during the months of July to December.


The entire municipality of Gamu except in some small spots in barangays District 1 and Upi are prone to liquefaction. Liquefaction occurs when a saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in which material that is ordinarily a solid behaves like a liquid.

The poorly drained fine-grained soils of the municipality such as the Bago Sandy Loam, Bago Sandy Clay Loam, Cauayan Sandy Clay Loam, and Cauayan Sandy Loam type of soils are the most susceptible to liquefaction. When earthquake shock occurs in waterlogged soils, the water-filled pore spaces collapse, which decreases the overall volume of the soil leading to collapse of buildings and infrastructures.

Alarming is the susceptibility of the municipality’s soil to liquefaction as from data gathered 98% are prone to liquefaction with only 2% free from liquefaction.

Landslide Hazard

Landslide whether rain-induced or earthquake-induced affects the municipality. Generally, a total of 11,238.94 hectares or 87% is not prone to landslide. Only 14% of the municipal land area is exposed to varying degrees of exposure. Table RM 11 shows the areas exposed to landslide hazard.