Along the ICE AGE FLOODS
NATIONAL GEOLOGIC TRAIL

17,000 years ago, a massive Ice Age lake – now called Lake Bonneville – filled a large portion of present-day Utah. As temperatures changed, the influx of ice melt caused the lake level to rise. In addition, the Bear River, once a tributary of the Snake, was diverted by volcanic activity back into Lake Bonneville. These factors ultimately led to the breaching of a sedimentary rock dam at Red Rocks Pass, Idaho. There was only one ice-age Bonneville Flood because Lake Bonneville broke through a rock dam, unlike the Missoula Floods whose glacial ice dam repeatedly dammed Glacial Lake Missoula, then broke and rebuilt.  1,100 cubic miles of Lake Bonneville water rushed through the Snake River Canyon, and it took only six weeks for Lake Bonneville to empty the equivalent volume of modern-day Lake Michigan. The Great Salt Lake we know today is a remnant of Lake Bonneville, but at one tenth the size, it is a mere puddle compared to what the lake used to be.  The power of this catastrophic flood widened canyons as the force of the water pulled huge chunks of basalt off the cliffs and tumbled them around, smoothing their jagged edges along the way. As the canyon width narrowed, the force and velocity of the flood increased. Wherever the canyons widened, the flood lost force and velocity, the waters slowed and began dropping its bedload – in this case, giant tumbled basalt boulders instead of your typical river gravel.  These flood-rounded boulders, named melon gravel due to their distinct shape, are scattered over vast areas of land. The rocks’ unique outlines and smooth surfaces caught the eye of Native American tribes in the area, who have used them as canvases for petroglyphs for thousands of years. Visitors can see the medium sized flood deposits just outside the visitor center, or hike upriver to see gigantic melon gravel the size of heavy-duty trucks.  Celebration Park is located in the Snake River Canyon, approximately 23 miles south of Nampa, Idaho. It is home to an enormous melon gravel field deposited by the Bonneville Flood.