The greater portion of eastern Cagayan and the foothills of the Cordilleras in the west are undifferentiated mountain soils. These areas total 393,740 hectares or 43.74% of the total area of the province.
Parts of the moderate slopes to moderately steep land, about 311,670 hectares or 34.62% of the total area of the province, are essentially loam of sandstone and igneous rock parent material.
Parts of the flat to nearly level land, some 165,420 hectares or 18.37% of the total area of the province is predominantly clay of alluvial parent material. Hydrosol, bog deep, beach sand, river wash, sand dunes, and rocks are approximately 29,440 hectares or 3.27% of the total area of the province. This last type is apparently free from soil erosion. The flat, nearly level lands along the rivers and creeks are however annually subjected to river erosion as the bodies of water traverse through the province. As the rivers move, municipalities may either experience accretion on one side and erosion on the other side of the rivers.
The steep and the very steep lands at the foothills of the Cordilleras are severely eroded, especially in those parts without vegetative cover found in the towns of Rizal and Sto. Niņo. This is also true for some parts of the Sierra Madre Mountains. Hence, the Cagayan River is heavily silted in some parts because of the topsoil carried by the runoff from these slopes. Abundant runoff means reduced infiltration, and reduced aquifer and spring recharge, adversely affecting water supply sources for domestic and irrigation purposes, especially during the hot, dry summers. These are the conditions that are currently being addressed by the on-going reforestation and afforestation projects by the national, provincial and municipal governments.