Geology and Relief: Gombe State is part of the central Nigeria highlands; but the flat landscape in the northern and southern parts of the state have isolated hills. While the elevation of the plain is at about 600m above sealevel, the hills reach between 700m and 800m.
Killang Hills, Kaltungo
The Gongola River is the main drainage system, running approximately northsouth towards the Benue River Basin, but with principal tributataries draining from west to east into River Gongola. Gombe State is geologically a part of the Upper Benue Trough, although the state is an entity of its own, the Gongola Trough. As such, the state con stitutes a major sedimentary basin, with a fill of about 6,000m of CretaceousTertiary Sedimentary rocks.
These rocks are well exposed throughout the state and have been recently explored for oil and gas, but without success. The eastern part of Gombe State is geological ly older than the west.
Exposures of the non marine Bima Sandstone, a sequence of Albian coarse sandstones, occur extensively in the south eastern part of the state, succeeded westwards by the transitional beds of the Cenomanian Yalde and Jessu Formations.
These are overlain by the Marnne Cenomanian to Caniacian shales and lime stones of the Pindiga Formation, followed by the Gombe Sandstone of Late Cretaceous age. Half of Gombe State is underlain by the Early Tertiary Kerri Kerri Formation of estuarine origin comprising sandstones, siltstones and ironstones.
The Chad formation, a sequence of continental silts and clays of lake origin and Late Tertiary age, covers the northern onethird of the state. Gombe State lies mostly within the poor groundwater provinces in the Gombe Sandstones, the Pindiga shales; KerriKerri Formation of Tertiary Age and the isolated hills region of the northern
central and southern parts. Groundwater occurs between 0180m depth on the sandstones. In the Gongola River Basin sedimentaries, because of the cretaceous sandstones and shales, groundwater is generally erratic and meagre.
The Palace of Emir of Gombe
Indeed, dams from suitable surface drainage systems would be more profitable and economical than groundwater and boreholes as sources of water for domestic, agri cultural and industrial use in the State. River Gongola is the only major river that traverses the state in the north and east through Dukku, Nafada and all the eastern LGAs, to join the River Benue at Numan.
At Nafada, the Gongola bends in a loop southward and flows through much of the eastern border of the State before it joins River Benue at Numan, outside the state. It is the sixth longest river in Nigeria, being about 530km, much of which is within Gombe State.
It has numerous tributaries and smaller streams in the state includ ing Rivers Dukul and Ruhu in the north (Dukku LGA). In the westcentral part, there are some trib utaries of River Guji, while in the southern parts of the state (including Balanga, Billiri, Kaltungo and Shongorn LGAs) the headwaters of several minor tributaries of River Benue characterise the land scape. They include Rivers Balanga and Dadin kowa.
Thus, the state is within the wider Benue Drainage Basin, with the dominance of the western part of the Gongola (sub) basin. As a result of its geological and geographical features, Gombe State has a large and wide variety of solid mineral deposits, abundant grazing fields and fertile agricultural land.
Soils And Vegetation: The neoloav of GomheState has exerted an enormous influence on soil development; hence over half of the state (central) that is underlain by the Kerri Kerri Formation has shallow to moderately shallow impoverished soils, with sandy loams on iron pan. On the Chad Formation in the northern part of the state, the soils are deep but sandy, and developed on clays and silty clays; but are mostly blanketed by sand dunes.
Soils in the eastern part of Gombe State are shal low to deep loamy, sandy clay, loam and vertisols with cracking clays that have weathered from shales. Vegetation in Gombe State is predominantly wooded shrubland in the central part, with the plant community comprising Anogeissus/ Combretum/ Affrormosia/Detarium.
The northern part of the State exhibits a mosaic of shrubbed grassland and grassed shrubland with the preponderance of Acacia. In the hilly southern areas, the vegetation is shrubbed woodland with mostly Affrormosia and Detarium. Gombe State has the cultivated and urban areas constituting over 35 per cent of the land use/land cover.