Pre-contact Alola shined with golden walls, made from tough yet thin strands of Dugtrio hair. Alola has no native quarries, but the presence of Dugtrio long allowed its people, even before the age of international trade, to build from metal as well as wood. Dugtrio were (and rarely, still are) shorn by farmers like a metal, non-electrified version of Mareep, and much of the region's elaborate network of caves is believed to have originated as Dugtrio farms.
Foreign sailors, who viewed Alola from their ships, mistook the metal of Dugtrio hair which supported its palaces for actual gold, at least until they could hold it in their hands. Dugtrio hair, after all, is made from a surprisingly light metal. Once its origins are discovered, this fact is unsurprising: the Dugtrio which carry so much hair on their heads are no Machamp or Buzzwole. Alolan Dugtrio are twice the weight of their counterparts elsewhere, not twenty times or more.
Yet these aspiring conquistadors sought to conquer Alola before they had the chance to place their hands on Dugtrio hair. Although they were defeated every time, Alola, too, lost many fine warriors in the struggle. Even while the news spread of what Alolan "gold" was made of, Alolans began to value the newly accessed foreign metals in the same way that the world they were joining valued real gold. So they continued to tear down buildings made of Dugtrio hair, or at least to hide them behind grayer exteriors.
The Dugtrio farms were abandoned, with few reminders in the present day, and the use of Dugtrio in construction was forgotten even by most Alolan historians. Yet whenever Dugtrio feel too forgotten, they use their extensive tunneling ability to unearth yet another ruin: archaeological bonanzas covered in the hair of their ancestors!