Final answer:
The largest gorge formed by the westward-flowing rivers and streams cutting through the Sierra Madre Occidental mountains is the Grand Canyon of the Colorado River.
Step-by-step explanation:
The largest gorge formed by the westward-flowing rivers and streams cutting through the Sierra Madre Occidental mountains in Mexico is the Grand Canyon of the Colorado River. It is a renowned natural wonder located in the southwestern United States. The Grand Canyon is a deep and majestic gorge that stretches for approximately 277 miles and has a maximum depth of about 6,000 feet.