The correct answer is option 1, i.e, Only 3. Colorado River: Hoover and Boulder Dam are the main dams on Colorado River. Imperial valley of the Colorado River is an important region for cotton cultivation. The outflow of Colorado River is Gulf of California. Tributaries: Little Colorado Source: Grand Country Its drainage basin covers 246000 square miles and includes parts of 7 states: Wyoming, Colarado, Utah, New Mexico, Nevada, Arizona and California. The longest of these unbroken trunk canyons through which the Colorado flows in the spectacular Grand Canyon, extending from the mouth of the Paria to the Grand Wash Stream. The river drains a vast arid and semiarid sector of the North America continent. Because of its intensive development it is often referred to as the "Lifeline of the Southwest".