The geology of the area is dominated by Pilliga sandstone , a coarse red to yellow Jurassic sandstone containing about 75 % quartz , 15 % plagioclase and 10 % iron oxide , although local variations in soil type do occur .
This is a coarse red to yellow Jurassic sandstone containing about 75 % quartz , 15 % plagioclase and 10 % iron oxide .