Cagayan is a vast expanse of plains and valleys, bordered by mountains, running north to south both on its east and west ramparts. It is crisscrossed by rivers and creeks, the largest of which is the Cagayan River, which originates from from the Province of Nueva Vizcaya with a drainage area of about 27,300 sq. kms. and a groundwater reserve of 47,895 mcm. and traverses the province from south to north. The larger tributaries of the Cagayan River are the Pinacanauan River in Peņablanca in the southeast; the Dummun River in Gattaran and the Pared River in Alcala, both in central Cagayan; and the Zinundungan River in Lasam and the Matalag River in Rizal, both in the west. The other rivers in the province are the Chico River in southwest Cagayan at Tuao, the Pata River and Abulug River in the northwest, Buguey River in the north, and the Cabicungan River in the northeast. These rivers drain the plains and valleys of the province, and provide water for domestic and irrigation purposes, as well.

Beyond the Sierra Madres to the east, the coast fronting the Philippine Sea has strips of level land that could be utilized for economic activities. However, only Bolos Point in Gattaran is presently accessible and is being used as a small port. There are several other prospective ports on the Pacific Coast, most notable of which is Valley Cove in Baggao. Similarly, the northeastern and northwestern parts of Cagayan are strips of level land, hemmed in by the sea on the north and by the mountains and hills on the south.

Of its total land area, 28.19% or 253,831 hectares are flat to nearly level land. This consists of alluvial plains, river deltas, low wetlands, mangroves, and beaches. Most of these are found contiguous to the bodies of water, especially along the Cagayan, Pared, Dummun, Pinacanauan, Abulug, and Chico rivers. These areas are planted to rice and corn, subjected to frequent floods during the wet season.

The gentle and moderate slopes of the province, which constitute 6.08% and 13.48%, respectively of the total land area of the province are mostly contiguous to the level land, enclosing the plains of the meandering rivers and creeks. This arrangement forms the various dales or valleys found in between the hills of the province.

Majority of the rolling land to moderately steep areas which account for 17.07% of the province's total area are found at the foothills of the Sierra Madre and Cordillera mountains, separating the valleys and the mighty ranges.

Steep and very steep land which constitute 10.44% and 24.73%, respectively, of the total land area, or 94,030 hectares and 222,595 hectares, respectively, are found along the Cordilleras, in some parts of Sta. Praxedes, Claveria, Sanchez Mira, Pamplona, Lasam, Sto. Niņo, and Rizal; and in the eastern parts of Santa Ana, Gonzaga, Lal-lo, Gattaran, Baggao and Peņablanca, as the northern mountains of the Sierra Madre range.

The Babuyan group of islands, which include the islands of Calayan, Babuyan, Dalupiri, Balintang and Camiguin, has a mixture of flat to nearly level land, and steep to very steep slopes. These islands have extensive coral reefs. There are two volcanoes in the Babuyan Islands: Mount Didicas off Camiguin island, which has a symmetrical cinder cone, about 215 meters above sea level, and Mount Pangasun in Babuyan island, which is about 840 meters above sea level and has two craters.

Another volcano found in Cagayan is Mount Kagua in Gonzaga in the northeast. It is being considered as a potential source of geothermal energy.