The caterpillar was crossing the Camel Back firetrail. I've selected 12 to 25 mm in size but it could have been a little larger - definitely under 50 mm though.
The photo resembles that of Anthela basigera at http://lepidoptera.butterflyhouse.com.au/anth/basigera.html which is one of a group of 4 related Anthela species: Anthela basigera occurs in Victoria, and South Australia. Anthela denticulata occurs mainly in southern Victoria. Anthela euryphrica occurs in mainly central New South Wales. Anthela oressarcha occurs mainly in the mountain areas of southern New South Wales, so I think it is most probably Anthela oressarcha.