For Kai Tahu, the boulders are not geological curiosities but evidence of a specific event. The Araiteuru, a great ocean-going waka, was sailing south along the coast in search of precious greenstone when it foundered near what is now Shag Point, known in Maori as Matakaea. The cargo washed ashore: eel baskets, calabashes, and kumara scattered along the beach. The rocky shoals extending seaward from Shag Point are understood to be the petrified hull of the canoe, and a nearby rocky promontory represents the body of the captain. The cracked, web-like patterns visible on many of the boulders are the remains of the canoe's fishing nets. This stretch of the Otago coastline carries the name Te Tai-o-Araiteuru, the Araiteuru coast, and each boulder on the beach represents a specific item lost in the wreck. The boulders are called Te Kaihinaki in Kai Tahu tradition, a name that connects them to the round food baskets and gourds that were the canoe's provisions.

The geological explanation requires a different kind of patience. During the Paleocene epoch, roughly sixty million years ago, the seafloor where these boulders now sit was covered in marine mud. Calcium carbonate began to crystallize around nuclei in the sediment, growing outward by mass diffusion rather than fluid flow, which is why the boulders are so remarkably spherical. The process was extraordinarily slow. The largest boulders, measuring up to two metres in diameter, are estimated to have taken four to five and a half million years to reach their full size, accumulating layer upon layer of calcite while ten to fifty metres of additional mud settled on the seafloor above them. After the concretions had fully formed, large internal cracks called septaria developed, radiating outward from hollow cores. When a drop in sea level allowed fresh groundwater to penetrate the surrounding mudstone, these cracks filled with brown calcite, yellow calcite, and traces of dolomite and quartz, creating the honeycomb patterns visible in eroded boulders today.

The boulders did not arrive on the beach. The beach came to them. Coastal erosion has been slowly eating into the mudstone bluffs behind Koekohe Beach, freeing the concretions from the sedimentary rock that enclosed them for tens of millions of years. As the softer mudstone weathers away, the harder boulders emerge and eventually tumble to the shore, where waves roll and polish them. The process is ongoing; new boulders continue to appear from the eroding cliff face. About one-third of the boulders on the beach range from half a metre to a metre in diameter, while the remaining two-thirds measure between 1.5 and 2.2 metres across. A few are slightly elongated, stretched parallel to the bedding plane of their former mudstone prison. Similar septarian concretions exist elsewhere in the world, in the Kimmeridge Clay and Oxford Clay formations of England, and at scattered sites across several continents, but few match the size, concentration, and dramatic coastal setting of the Moeraki Boulders.

In 1848, geologist and politician Walter Mantell sketched Koekohe Beach and its boulders. His drawing, now held in the Alexander Turnbull Library in Wellington, shows considerably more boulders than visitors find today. Some have been broken apart by the sea. Others have been carried off by souvenir hunters or damaged by visitors over the decades. The boulders that remain are now protected within a scientific reserve, and the site has become one of the most visited natural attractions on the South Island. Tourists arrive at all hours, though sunrise draws the largest crowds, when the low-angle light turns the grey spheres golden against the dark sand and the Pacific stretches flat to the horizon. The cracked-open boulders are the most photographed, their septarian interiors exposed like the cross-section of some alien fruit. Stand among them at dawn, with the tide pulling back, and the Araiteuru story feels less like legend than memory.