About 900 million years ago, a magma (molten rock) was introduced into fractures in much of the rock east and west of Alice Springs. The fractures were vertical and extended north-south. This intrusion of magma opened the fractures. The magma cooled and formed a dark green rock called ‘dolerite’. At Standley Chasm the dolerite intruded the Chewings Range Quartzite (now comprised of interlayered quartzite and mica schist). Dolerite is much less resistant to weathering and erosion than quartzite. During the latest weathering cycle a south-flowing creek has eroded one of these dolerite dykes leaving vertical quartzite walls, which are now the walls of Standley Chasm. No dolerite can be seen in this chasm; however, a dolerite dyke can be seen on the side of the road approximately 2.2km from the kiosk at the top of the hill, just past the large creek crossing.
(from a Northern Territory Government geological Survey, that was distributed by the Department of Mines and Energy)
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