Mawddach Group

Mawddach Group Stratigraphic range: mid to late Cambrian
Slates of the Dolgellau Formation exposed in the Golwen quarry, near Fairbourne
Type	Group
Sub-units	Dol-cyn-Afon Formation, Dolgellau Formation, Ffestiniog Flags Formation, Maentwrog Formation, Clogau Formation
Overlies	Harlech Grits Group
Thickness	about 2400m
Lithology
Primary	mudstones
Other	sandstones, siltstones
Location
Region	northwest Wales
Country	Wales
Type section
Named for	Afon Mawddach (river)

The Mawddach Group is a middle to upper Cambrian lithostratigraphic group (a sequence of rock strata) in Gwynedd, Wales. The name is derived from the river known as the Afon Mawddach.

The rocks are exposed across the Harlech Dome and southern Snowdonia.

The Group comprises around 2400m thickness of mudstones, sandstones and siltstones laid down in the marine Welsh Basin during the middle to late Cambrian period. The Group comprises (in descending order i.e. oldest last) the Dol-cyn-Afon Formation, the Dolgellau Formation, the Ffestiniog Flags Formation, the Maentwrog Formation and the Clogau Formation.