This extensive association occurs:
In valleys on the west coast,
In the Tenom, Keningau, Tambunan, Sook and Pedawan Plains,
On the northeast coast from the Bengkoka Peninsula to the Sugut estuary,
In the Labuk estuary,
Along the Kinabatangan downstream from the confluence of the Kuamut and the Millian,
Along the south coast of the Dent Peninsula,
In the Semporna Peninsula, and
Around Cowie Harbour.
In the Segama valley, it is restricted to the Tomanggong Estate. It also occurs near Sandakan Airport (Eg. Kg. Batu Putih, Kg. Sg. Kayu, etc.).
The association occurs on terraces of old alluvium at heights ranging from near sea level to over 450 m in the inland plains. It reaches 510 m in the Labau valley. The terraces are, in general, flat to slightly undulating with short steep slopes in dissected parts. The alluvium is mainly medium- to fine-textured but is occasionally coarse-textured and stony.
The alluvium is mainly medium, rarely fine, in texture and in places contains variable amounts of pebbles. Deep pebble deposits also occur. The pebbles are mainly of quartz and sandstone but in addition are formed of chert in the Kuamut area, acid igneous rocks and chert at Tomanggong and basalt in the Menanam Plain.
Lowland dipterocarp forest covers much of the association and is often rich in Eusideroxylon zwageri while heath (kerangas) forest occurs sporadically. Sample plots in the Lokan valley recorded Koompasia malaccensis, Dyera costulata, Shorea exellitica, Dipterocarpus confertus, Dipterocarpus pachyohyllus and Scaphium macropodum as large emergent trees up to 54 m in height. Species of the middle storey included Ganua kingiana, Dacroydes rostrata, Myristica villosa, Sterculia treubii and the understorey included Mallotus penangensis, Polyalthia sumatrans, Baccaurea puberla and Parinari asperula.