The correct answer is option 1: Colorado River. The Grand Canyon is located in the southwestern United States, specifically in the state of Arizona. It is formed by the Colorado River over millions of years of erosion. The Colorado River flows through the canyon, cutting through layers of rock and creating the deep and dramatic landscape that we see today. The Grand Canyon is one of the most famous natural landmarks in the world and attracts millions of visitors each year. It stretches for approximately 277 miles and is known for its breathtaking views and unique geological formations. It is important to note that options 2 (Rhine River), 3 (Tapi River), and 4 (Niger River) are incorrect because the Grand Canyon is not located on any of these rivers.