Over 400 million years ago the sea covering the area receded. It left behind a layer of yellowish marine siltstone and sandstone rocks. Around 66 million years ago non-marine sediments left a sandy layer behind. Over time the ancestral valley of the Merri Creek developed, eroding through these sediments. Then, from 4.6 to 0.8 million years ago volcanoes such as Hayes Hill (about 5 km east of Donnybrook) and Mount Fraser (near Beveridge) erupted, sending lava on a journey along the ancestral valleys of the Merri and Darebin Creeks and into the valley of the Yarra River as far as the CBD.