From its headwaters on Two Ocean Plateau in Yellowstone National Park, the Snake River flows north to south through the park, entering Jackson Lake near the boundary of Grand Teton National Park and John D. Rockefeller, Jr. Memorial Parkway. The Snake River then flows through the spillways of the Jackson Lake Dam and from there southward through Jackson Hole, exiting the park just west of the Jackson Hole Airport. The largest lakes in the park all drain either directly or by tributary streams into the Snake River. Major tributaries which flow into the Snake River include Pacific Creek and Buffalo Fork near Moran and the Gros Ventre River at the southern border of the park. Through the comparatively level Jackson Hole valley, the Snake River descends an average of , while other streams descending from the mountains to the east and west have higher gradients due to increased slope. The Snake River creates braids and channels in sections where the gradients are lower and in steeper sections, erodes and undercuts the cobblestone terraces once deposited by glaciers.