The Silabukan association occurs:
north and west of Sandakan,
from the Lokan River to Gomantong,
from between Sg Pin and Sg Lamag westwards to Sg Malua,
in the Bangan Basin, and
in the Inarat lowlands
It occurs on low hills and valley floors, with amplitudes less than 15-30 m and with a regular pattern of dissection. Slopes range from 0-25° but are commonly in the 10-15° range. The association is similar to the Lungmanis Association but the hills are slightly higher and the valley floors are much narrower.
The soils are developed on those parts of the Tanjong and Sandakan Formations where mudstone is predominant, but is interbedded with sandstone. Quartz and sandstone pebbles, often in the form of stonelines, occur sporadically and are considered to be colluvial remnants of once more extensive terrace deposits. They have been observed north of the Kinabatangan at Lamag, north of Sandakan and in the Lokan Valley. In addition, both fine-end coarse-textured alluvium occur on the valley floors.
Dipterocarp forest is the natural vegetation. However, large areas have been converted to oil palm plantations. Around Sandakan, small farms, gardens and rubber estates have been in existence since the early 1900s.