Complex sentence: Many tribes on the eastern border with Nevada are classified as Great Basin tribes, some tribes on the Oregon border are classified as Plateau tribes, and tribes in Baja California who do not cross into California are classified as Indigenous peoples of Mexico.
Split into simpler sentences: Many tribes on the eastern border with Nevada are classified as Great Basin tribes, and some tribes on the Oregon border are classified as Plateau tribes. Tribes in Baja California who do not cross into California are classified as Indigenous peoples of Mexico.