Ordovician age Pittman Formation
greywacke and
turbidites are found in the far east and northwest including a band of Acton
Shale occurring right on the eastern border of the suburb. Next in the centre, south and north west of Giralang there are late
Silurian sedimentary rocks. From the east to west there are,
mudstone, State Circle Shale, and then
micaceous Black Mountain Sandstone that contains lenses of shale. In the south west of Giralang is calcareous shale from the Canberra Formation. A long fault heading north west roughly parallel to Ginninderra Creek is marked on the surface by an iron oxide reef. In the south of Giralang this fault separates the Canberra formation from State Circle Shale uplifted on the east side. ==References==