The low rolling hills of Cannon Hill were formed from sediment laid down under the sea between 210 and 180 million years ago.
Alan Cunningham's map of the Brisbane River shows Cannon Hill as open forest hills. Much of the area is high and cool, with breezes from the river and bay, although the area north of Wynnum Road is flatter and lower, and between Barrack and Junction roads was originally largely tea-tree swamp. The plentiful water from creeks and waterholes provided an abundance of flora and fauna. Where there now is a concrete drain along Todman Street, there once was a string of waterholes, named 'Naked Gully' because of the youths who swam there.
Along Richmond Road are a few remnants of semi-intact original eucalypt forest: ironbarks, spotted gum, bloodwoods, stringy barks, and grey gum with a grassy, mixed, or shrubby understorey. Cannon Hill has the largest colony of squirrel gliders in south-east Queensland.