Stratigraphy: The Quaternary is the most recent, and the shortest, geological period, extending from about 1.6 million years ago to the present day.

Distribution: Alluvium occurs along most river valleys, but is especially extensive in the western and northern New Territories on the Fanling and Yuen Long plains. Colluvium is a widespread hillslope deposit, but the thickest accumulations commonly occur in isolated upland valleys and on lower slopes.

Lithology: Alluvial deposits typically consist of well-sorted to semi-sorted clay, silt, sand and gravel. Colluvial deposits are generally poorly sorted and commonly comprise a slightly clayey sandy silt to gravelly silty sand matrix enclosing angular to subangular weathered boulders.

Depositional Environment:Alluvium accumulates in and adjacent to river channels, whereas colluvium is deposited by mass wasting processes acting on hill slopes.

(Middle Pleistocene to Holocene alluvial deposits (Chek Lap Kok and Fanling formations), Po Chue Tam, Tai Po.)