[5][6] Fort Rock was created when basalt magma rose to the surface and encountered the wet muds of a lake bottom.

Powered by a jet of steam, molten basalt was blown into the air, creating a fountain of hot lava particles and frothy ash.

Steam explosions also loosened angular chunks of black and red lava rock comprising the valley floor.

Waves from the lake waters eroded the outside of the ring, cutting the steep cliffs into terraces 66 feet (20 m) above the floor of Fort Rock Valley.

This coincides with a period of time when large pluvial lakes filled the valleys of central Oregon and much of the Great Basin of the western United States.

They resemble impact craters formed by meteorites, but lack the heavy metal signature residues of space objects.