The Colestin Formation is a unique geological expression within a short walking distance of Singing Falls. It is just one of the many different and subtle influences on the ecology of the region. An explanation of this formation can be found in the Tiller District Assessment. Click on the link to download the PDF.

(Oligocene and upper Eocene) Thin to moderately thick bedded, coarse- to fine-grained arkosic and micaceous sandstone and siltstone, locally highly pumiceous, of the marine Eugene Formation; and coeval and older andesitic lapilli tuff, breccia, water-laid and air-fall silicic ash of the continental Fisher and Colestin Formations; upper parts of the Fisher Formation apparently lap onto and interfinger with the Eugene Formation.