Two cones of glassy lava lie directly south of this location, with the largest rising 800 feet above the surrounding plain. Hot molten lava erupting from great depth met cold surface water in the wet flood plain of Snake River, and the northern butte formed in the channel of Henry’s Fork, which was forced farther east. Suddenly chilled into small particles of volcanic glass, the lava exploded upward in a great spray of steam and solid fragments that built into wind-blown cones around large summit craters a half mile long and 200 to 400 feet deep.