When opal was finally discovered in this country in 1915 - by prospectors who had come looking for gold - the diggings that sprang up took the name the explorer had left behind. For years the settlement was known simply as the Stuart Range Opal Field, before locals settled in 1920 on the name everyone uses now: Coober Pedy, from the Kokatha words usually rendered as 'white man's hole'. But the range kept Stuart's name, a fitting tribute to the man who came so close to the prize and walked away empty-handed, never realising what lay beneath the flinty pavement that had punished his horses.

The Stuart Range is barely a range at all - a low upland running about 170 kilometres from north-west to south-east, passing within ten kilometres of Coober Pedy. Its real drama is in its layers. Beneath it lies the Bulldog Shale, grey marine mudstone laid down in the Early Cretaceous, when an inland sea covered this part of Australia more than a hundred million years ago. That ancient seabed is exactly why the opal is here: silica dissolved from the weathering rock seeped down through the sediment and slowly hardened in cracks and cavities, sometimes filling the shells of long-dead sea creatures with gemstone.

Stuart's flinty stones have a name too: silcrete, a rock-hard crust formed as dissolved silica re-cemented loose sediment into sheets near the surface. Over immense spans of time, as wind and water stripped away the softer ground, this silcrete was left behind as a scatter of gibbers - the 'desert pavement' that tiled the plains and tortured the explorer's horses. The crust acts as armour, shielding the weaker earth below from erosion and giving the landscape its flat, undulating character. Where streams have cut through, they leave behind flat-topped mesas and buttes, each capped with silcrete until that final hard layer finally wears away.

For all its modest height, the Stuart Range plays an outsized role in how water moves across this country. Through the Tertiary period it served as a major drainage divide, separating the ancient river systems of the Eucla Basin from those feeding toward Lake Eyre. Today the multi-hued colours of the bleached Bulldog Shale give the Arckaringa and Stuart Range landscape a painted, picturesque quality - the same weathering that created the opal also stained the country in soft bands of ochre, grey, and white. It is a quiet, low ridge that asks nothing of the eye, until you learn what it took an explorer's misfortune to overlook.