The northern and eastern regions of Tabin are characterised by flat or gently undulating lowlands between sea level and 100 metres in altitude. Except for the swampy north-eastern quarter there are small hills between 150 and 250 metres high scattered throughout these lowlands, particularly in the areas bordering the central Tabin massif.
The central, southern and western highland regions of Tabin comprise, sedimentary-volcanic formations (see Map, above right). This rock type also covers most of the western half of the northern lowlands except for the southern flanks of the Segama River Valley which are overlaid with alluvium and peat. Alluvium and peat also cover most of the low-lying north-eastern quarter of' Tabin including the lower portion of the Tabin river valley. To the immediate East of this valley is an area of sedimentary formations. North of that there are a few intrusions of volcanic rock. Sedimentary formations or alluvium and peat accounts for the rock types of the remainder of the Dent Peninsula east of Tabin.
Soil types in Tabin consist predominantly of varieties of mudstones and sandstones, mixed with miscellaneous rocks. There are also fairly large areas scattered throughout the reserve that consist of tuffaceous rocks interspersed with mudstone and sandstone. Some of the flatter river valleys and swampy areas in the north-east of the reserve have alluvial soils or a mixture of alluvium and peat. Bordering such areas in the interior of the north-eastern quarter are patches which consist of a mixture of mudstone and alluvium. Several small ranges of hills in the centre of the northern region have limestone soils but compared with some other areas in eastern Sabah Tabin has very little of this soil type.