What has called into question California and the southwest region's ability to sustain the lifestyle of its residents?

It's hard to generalize about the cultural practices of indigenous people in the West since its climate and resources varied immensely, creating microenvironments which different groups used to their advantage. Over one hundred federally-recognized tribes lived in modern California. The Great Basin—the vast expanse of land between the Rocky Mountains and the Sierra Nevadas—was home to the Mono, Paiute, Bannock, Shoshone, Ute, and Gosiute peoples, among others.

Explanation:

c: haven't lost any yet