There are four species of grass tree with underground trunks in this area, and one species with a trunk above ground, Xanthorrhoea glauca, that could look like this when young. Telling them apart is fiendishly difficult, depending on characteristics of the bracts surrounding individual flowers and between individual flowers in the spike.
This is unlikely to be X. glauca angustifolia, a species found a little further inland, west of the DV, the only potential species found in this region are: Xanthorrhoea concava Xanthorrhoea australis Xanthorrhoea resinosa