Below this point, the Colorado River makes a dramatic turn. Since entering Grand Canyon at Lees Ferry, it had been deepening its gorge east of the Kaibab Plateau. Here the river turned west and cut straight through the plateau, opening a gateway that allowed it to carve the deepest section of Grand Canyon, the Granite Gorge. In 1861, John Strong Newberry, identified as the first geologist to visit the canyon, concluded that the Colorado River had carved the canyon, and that finding still holds today. Why the river turned to slice through the plateau remains a puzzle geologists continue trying to piece together as they reconstruct Grand Canyon's evolution, but continued erosion confounds them because many clues are swept away by the river into the Gulf of California and remain hidden in the delta.