Although the Colorado river has obviously cut down through the layers of rock why were scientists unsure that this explained how some areas of the grand canyon formed?

Scientists were initially unsure that the Colorado River alone was responsible for the formation of certain areas of the Grand Canyon because the canyon's complex geology and the presence of various rock layers suggested additional geological processes at play. Factors such as tectonic uplift, erosion from other sources, and the influence of ancient river systems may have contributed to the canyon's intricate features. Additionally, the timing of the river's incision and the age of the rock layers raised questions about the river's role in shaping the landscape. These complexities led to ongoing debates about the canyon's formation.