Viewed from the George's River, Lugarno rises majestically out of the water, the steep hillsides adorned with the red barked Angopheras. From the top of Punt Hill the land is comparatively level, sloping gently towards Peakhurst, until it suddenly drops down Chivers Hill.
On the western side of this sandstone plateau is the broad expanse of the tidal Salt Pan Creek, and on the eastern side is Boggywell Creek, leading into Lime Kiln Bay.
The George's River has cut deep into the sandstone, however large amounts of sand have settled on the bed of the river, making the water shallow. The river at Lugarno is tidal, rising and falling a little later than the tides in the ocean.
How did this landscape develop?
The sandstone which is the most common rock found in Lugarno is known to geologists as Hawkesbury Sandstone. It was laid down in a shallow sea during the Triassic period which ended 180 million years ago. The grains of quartz were cemented together by clay and silica, and were formed into rock by the pressure of more sediment being deposited on top of them. The Ashfield or Wianamatta Shale was laid on top of the sandstone.
While these deposits were being laid down, they were being gently lifted out of the sea. The rocks dried out and became subject to erosion in a climate that was more humid and wetter than it is now.
The George's River was formed, and carried a great deal of the shale out to sea as it was being eroded away. The surface of the land was fairly flat with shallow river valleys.
A volcanic neck intruded into the rocks of Lugarno, near where Evatt Park is now, about 50 million years ago (the early Triassic period). E.T. Kenny did a geological survey of the area in 1929 and found:
" The neck occupies a conspicuous depression within the Hawkesbury sandstone. In the deepest portion of the valley, the surface of the neck is from 75 to 160 feet below the ridge top, and about 100 feet above the level of the George's River.
In plan the neck is elliptical. it occupies an area of twenty acres approximately, the dimensions being 20 chains in length and 10 chains in width. The longer axis is arranged in an easterly and westerly direction.
A heavy waste sheet of sand and sandy loam, the outwash from the sandstone country, cloaks the position of the exact boundaries of the neck.
Boulders of volcanic breccia were observed within the neck, but no definite evidence of any lavaform type of rock was noted. In a shallow well a decomposed, basic rock evidently of volcanic origin, was intersected. This may be arranged as a dyke within the breccia.
Altered sandstone (quartzite or 'white metal') outcrops on the south side of the neck.
Near the Forest-road a lens of ironstained and white clay, in part sandy, is exposed within the massive sandstone." (A. Rep. Dep. Mines NSW for 1929, p.91.)
About 25 milllion years ago, the rocks around Sydney began to tilt to form the Sydney Basin. Over several million years this uplift produced the Woronora Plateau to the south of Sydney. As the land rose, the gradient of the George's River increased, and the river flowed quicker and with greater power of erosion, producing the steep gorges we see today.
During the Ice Age (from about 1 million years ago to 30,000 years ago) the sea level fell as water was taken into ice caps in other parts of the world. The sea level was then a few hundred metres below what it is today. The river cut even deeper into the gorges in order to reach the lower sea level.
From about 30,000 years ago the sea level began to rise, and the deep river valleys were flooded by the rising sea. This caused the silt and sand carried by the river to be deposited in the tidal regions of the river, and the formation of sand dunes which produced Botany Bay.
The geological map for Sydney shows two small areas in Lugarno where the shale has survived: one near the top of Chivers Hill, and another near the top of Punt Hill. Elsewhere the shale has been eroded away to expose the sandstone that lay underneath.
Erosion from creeks in Evatt Park, beside Ponderosa Place, and on Punt Hill has produced the present landform.