• Locality From near Quilty’s Mountain (Endrick Trig) in the Budawang Ranges, approximately 20 km S of Nerriga, southern NSW.

• Google Earth Search for "Quiltys Mountain, Corang NSW" 35°12’S 150°11’E

• Download https://www.google.com/earth/download/gep/agree.html?hl=en-GB

• Map Ulladulla (SI 56-13) 1:250K

• NSW Lands Dept Endrick (8927-4-S) 1:25,000

Background

The area is dominated by cliff-forming Early Permian sandstone and conglomerate overlying and underlying siltstone, which weathers to form slopes. Adjacent to Quilty’s Mountain, the siltstone forms the lowest units of the Sydney Basin succession. Towards the east, the lower cliff-forming sandstone is the basal unit of the Permian succession.

These nearly flat lying strata were deposited on an uneven erosion surface, developed on folded and eroded Devonian quartzite, volcanic rocks and Ordovician slates of the Lachlan Foldbelt. The straight valley (Vines Creek) on the eastern side of Quilty’s Mountain is partially filled by basalt - a vent can be defined.

What to do

Prepare a transparent overlay (geological map) of the area under stereo cover showing the main formations, geological structures and dominant joint trends using the aerial photo 5108 - right click on the image to the immediate left of this text paragraph (above if viewing by tablet or phone) and save the file to your desktop . Use this photograph as the map base; it is at a scale of approximately 1:85,000. The downloaded file should cover more area than shown in the image to the left.

By default, Google Earth tilts the view as you zoom in close. It is preferable to look straight down at the earth, but Google also gives an oblique view. (To straighten the view, to press the letter "R" on the keyboard.) To zoom without tilting, click "Tools" on the Google Earth menu. Another option is to 'Enter Flight Simulator' under the Tools menu.

Using oblique, or three-dimensional, view explore around the cliffs with a printed copy of the photobase next to you. Try to identify the geological elements described in the background (above). As a minimum, you should be able to define: (i) a cliff forming conglomerate around most of Quilty’s Mountain (look at the jointing); (ii) a lower siltstone (use the break in slope); (iii) a sandstone sequence that overlies the conglomerate (look for cross bedding features); (iv) valley filling basalt; (v) Ordovician and / or Devonian basement rocks.

• Carefully trace out the boundaries of the different geological units on an overlay to the aerial photograph, using a much detail as you can. Neatness is important in these exercises as neat traces are more accurate than cursory lines. Don't (lightly) colour in the geological units until you have annotated the map with other elements, for example morphological features, bedding strike and dip (see symbols on surface interpretation)

• Don't forget to prepare a geological legend and make sure you have all the elements of a geological map.

• Prepare an east-west geological cross section through an appropriate place on your photo interpretation, illustrating the 3D relationships of the various units. Indicate the start and end of the section on the map,

• Prepare a geological history table, based on the observations you have made.

Guiding questions

• Does the cliff line around Quilty’s Mountain vary in altitude? What might this indicate about the sloping ground below? - is it weathered rock or talus?

• Compare the topography of the western and eastern sides of Quilty’s Mountain. Note the valley of Vine’s creek, on the east, lacks a slope along the edge - it is higher than the wider Sallee Creek valley on the west. The Vines Creek valley also lacks a well-defined stream. These rather subtle clues indicate that the valley has been partially filled by basalt, flowing from a vent at the southern end of the valley. The difference between the basalt -filled valley and that draining south from the crater site is even more striking and shows the unusual nature of the former.

• Are there any likely relations between tones and rock composition?

• Is there any evidence of folding and/or faulting? What are the dominant joint directions on the plateau surface? Why are they so prominent in only some places? Why are they not faults?

• What changes do you notice in the upper cliff-forming sandstone from left to right across the images?

Branagan, D. & McNally, G., 1991. Australian Geology; Remote Sensing Exercises Manual. Geoscope, 55 pp.