Then the river then turns abruptly west directly across the folds and fault line of the plateau, through the Upper and Lower Granite Gorges of Grand Canyon, which is long and from between the upper cliffs. The walls, high, drop in successive escarpments of , banded in splendid colors toward the narrow gorge of the present river. The river itself is a nearly uninterrupted series of violent rapids separated by calm, short pools. Deep inside the canyon it is joined from the north by Kanab Creek, which flows from southern Utah, and then from the south by Havasu Creek, known for the waterfalls it forms on the Havasupai Reservation. Further downstream it passes the Uinkaret volcanic field, where basalt eruptions millions of years ago formed huge lava dams across the Colorado. Although the dams have mostly been erased by erosion, a small portion remains as Lava Falls, generally considered the most difficult and dangerous rapids for boaters on the Colorado River.