Like the larger Helmcken Falls, Spahats Falls owes its formation to deposits of volcanic rock in the Wells Gray-Clearwater volcanic field. Starting about 300,000 years ago, numerous eruptions from Trophy Mountain poured into the Clearwater River Valley and filled it layer upon layer to a depth of over . Eruptions in various parts of this valley continued sporadically for 200,000 years, producing some of lava and creating Wells Gray Park features such as Murtle Plateau. After the eruptions, the Clearwater River re-established its course and began cutting into the lava. During the Pleistocene, gigantic icefields scraped away at the lava. When all this ice melted, the floods completed the carving of Granite Canyon on the Clearwater River and the side canyon where Spahats Falls occurs.