The part of Williamsdale[5] in NSW[6] is itself split up by two Local Government Areas, in the north to Queanbeyan–Palerang and in the south to Snowy Monaro.

Quartz crystals make up 25%, plagioclase 5%, alkali feldspar 10%, biotite 5–10% which is altered to chlorite, epidote and leucoxene.

Middle Silurian Colinton Volcanics foliated dacite and tuff is under Williamsdale.

To the west of Williamsdale is an outcrop of Upper Silurian Laidlaw Volcanics dark grey rhyodacitic and dacitic crystal tuff.

They form a narrow band extending to the south as far as Cooma following on the east side of the Murrumbidgee River.