penshurst is located in an area littered with basalt stones up 2m long from the mount rouse volcano. these are known locally as the stony rises, the technical name being "breached barriers", having been formed from collapsed lava tubes. features similar to the stony rises may be observed in other areas of south-west victoria where there is a history of volcanic activity. the north east side of mount rouse is used as a quarry and crushed for road making scoria.