Archaeology Kit 101
A General Description of Sims 4 History as Portrayed in the Archaeology Kit
Prehistory happened everywhere, hence prehistoric artifacts can be found anywhere. However, some places have experienced more digging and building than others, and thus preserved lesser or greater amounts of prehistoric artifacts. Dry areas, like deserts, would tend to have more prehistoric artifacts and fossils.
The era of Ancient civilizations, which includes Al Simhara, is referred to in Smede (1) as Magnolian civilization as it was centered on the Magnolia River Delta. The Magnolia river runs through Willow Creek, as well as Newcrest and Magnolia Promenade. Ancient civilization wasn't confined to this region, however.
Medieval Sims civilization, as portrayed in Sims Medieval and Champs Les Sims, was centered around Windenburg, as portrayed in Archaeology Kit. The Ruins date from this time. Pirates were based in Brindelton, but also left artifacts along many of the coasts of Sim Nation, particularly in Sulani, due to the beautiful weather and Princess Cordelia's love for shellfish.
Traces of both the ancient Hou Dynasty of Shang Simla and the later Komorebian Shogunates can be found primarily around Mt Komorebi. But the ancient Sims Road provided a way for trade goods from these periods to find their way to many other regions (2).
And what to say about Sixam? Artifacts from the mysterious visitors can be found in places where they've frequently been sighted, or where other extraterrestrial activity is common. And on Sixam itself, of course.
1. The Ecclesiastical History of the Simlish People, Vol 1, by Venerable Smede
2. The Book of Hou, by Man de Zhao