WSW-ENE oriented trough known as the Snake River Plain. The river did not carve the Snake River Plain, but rather the Snake River took the course of least resistance and followed the path formed by the hot spot through the Rocky Mountains. The first lava flows started pouring out in what is now the western part of the Snake River Plain and is still extruding in the eastern part of the plain. Even larger lava flows of Columbia River basalts issued over eastern Washington, forming the Columbia Plateau southeast of the Columbia River and the Palouse Hills in the lower Snake. Separate volcanic activity formed the northwestern portion of the plain, an area far from the path of the hotspot The hot spot now resides beneath Yellowstone National Park. The heat from the molten rock beneath the park domes the crust up to form the Yellowstone Plateau The Snake River Plain and the gap between the Sierra Nevada and the Cascade Range together formed a "moisture channel," opening the way for Pacific storms to travel more than inland to the headwaters of the Snake River. When the Teton Range uplifted about 9 million years ago along a detachment fault running north–south through the central Rockies, the river maintained its original course and cut through the southern end of the mountains, forming the Snake River Canyon of Wyoming. About 6 million years ago, the Salmon River Mountains and Blue Mountains at the far end of the plain began to rise; the river cut through these mountains as well, forming Hells Canyon. Lake Idaho, formed during the Miocene, covered a large portion of the Snake River Plain between Twin Falls and Hells Canyon, and its lava dam was finally breached about 2 million years ago. Lava flowing from Cedar Butte in present southeast Idaho blocked the Snake River at Eagle Rock about 42,000 years ago, near the present-day site of American Falls Dam. A lake, known as American Falls Lake, formed behind the barrier. The lake was stable and survived for nearly 30,000 years. About 14,500 years ago, pluvial Lake Bonneville in the Great Salt Lake area, formed in the last glacial period, spilled catastrophically down the Portneuf River into the Snake in an event known as the Bonneville flood. This was one of the first in a series of catastrophic flooding events in the Northwest known as the Ice Age Floods.