TEKS E.5 (C), E.6 (A), E.2 (6A), E.2 (A), Fig. 19B - Read the text below and answer the question.
Some 20,000 years ago, mammoths and bison migrated to the Tularosa Basin grasslands in today’s New Mexico, followed by hunters and gatherers. The land began drying out, but ancient settlers could still harvest rice, grass, and maize. By 700 A.D., the rains returned and settlements grew. However, by 1350 A.D., the drought returned, and the settlements were abandoned.
Which best states the author’s theme?