5.6 Hills and low hills (Mount Arapiles)

A number of topographically significant and materially different features appear within the North West Dunefields and Plains as inliers. The major inliers include the largest inlier, Mount. Arapiles and associated outlier (Mitre Rock,) as well as Mount. Jeffcott and lower weathered Palaeozoic sediments often subsumed by surfical deposits. This is a similar category to that within the Northern Riverine Plains (unit 4.4).

The Mount Arapiles complex is to the west-north-west of the Grampian Ranges, relatively square in plan view with an area of approximately 15 km2. Slopes are characterised by steep to precipitous segments and a relatively flat summit at about 300 m elevation with a striking mesa at 369 m. The mountain itself is unlike the sharper strike ridges and valleys of the Grampian Ranges while composed of similar material and geological age. Mitre Rock occurs as an isolated monadnock of Grampians
sandstone to the north of Mount Arapiles. Mount. Arapiles is bound by the Douglas Depression (unit 5.3.3) to the west, north and south, as well as ridges with sand and flats (unit 5.5.2) to the south-east and clay plains (unit 5.4) to the east.

Mount. Arapiles is made up of resistant Grampians sandstone with the Douglas Depression diverted around it, indicating some form of structural control. It is abutted by stranded beach ridges, and a marine cut platform at its base is evident as part of the transgression/regression cycle of the Tertiary sea.