Why did linguist Edward Sapir consider California’s Indigenous languages especially diverse?

The American linguist Edward Sapir considered the Indigenous languages of California to be exceptionally diverse because the region contains representatives of approximately 20 distinct language families, including Uto-Aztecan, Penutian, Yokutsan, and Athabaskan.1

Sapir famously described this linguistic landscape as being more diverse than that found across the entire continent of Europe. This high level of linguistic variety is reflective of the region's complex geography, which features a mosaic of microenvironments—such as coastal forests, deserts, and mountains—that supported a dense and varied population of Indigenous peoples.12