The Rumidi Association occurs:
in the Sandakan and Kinabatangan Districts,
extending from the Labuk estuary in the northwest to the Sungai Segama in the south and southeast,
in the Kudat Peninsula, and
on Pulau Banggi.
It is formed on low hills and narrow alluvial flats with an amplitude of 15-30 m and short slopes ranging from 5-15° on the hills. There is no regular pattern of dissection because the slump formations from which the hills are formed are largely unstratified. The Garinono Formation which is most extensive consists mainly of slump breccia and included sequences of interbedded mudstone, tuff, tuffite and minor sandstone and calcarentite. The slump breccia is made up of fragments and blocks of assorted rocks in a mudstone matrix. Although the Garinono Formation is by definition complex, the majority of soils are formed from mudstone and sandstone often in the form of mixed colluvium. Mudstone and sandstone are particularly common near the Sg Segaliud, Sg Dumundong, Sg Koyah and north of the Labuk road.
Lowland dipterocarp forest is the natural vegetation of the association, but has been, or is in the process of being logged. Logged areas with Forest Reserves are in the early stages of regeneration. In the Sandakan District, large areas have been clear felled and a considerable acreage has recently been planted with oil palm.
The Rumidi Association is suitable for agricultural development.