About twelve thousand years ago, Fossil Falls lay in a much wetter landscape where large lakes filled nearby desert basins, glacier-fed creeks flowed from the Sierra, and the Owens River ran through basalt outcrops east of this site. Native American people lived here with access to fresh water, abundant plants and animals, and high-quality obsidian a few miles to the east. Rock foundations from homes, obsidian chips from toolmaking, and shallow grinding holes near the top of the falls show various occupations of the site between 12,000 and 3,000 years ago. The surrounding landscape was shaped by repeated volcanism dating back as far as 440,000 years ago, when eruptions from the Coso Mountains spread basalt across the area and formed scoria as well. During the last ice age, large lakes formed in regional basins, the Owens River flowed south out of Owens Lake into Indian Wells Valley, and eruptions from the Coso Range changed the river's course at least three times. Fossil Falls formed when an eruption dammed the Owens River and sent it over basalt flows, where the water sculpted and polished the black rock into a two-tier dry waterfall with a forty-foot drop at the first tier and a second tier nearly two hundred feet below.