The Rospuda flows through typical young glacial landforms: postglacial channel lakes, eskers (long, narrow, winding ridges composed of stratified sand and gravel), and flat outwash plains.

The erosion found at Fossil Falls was formed by the youngest glacial runoff, called the Tioga, from the Sierra Nevada Mountain Range about 20,000 to 10,000 years ago.

Furthermore, these regions of older drift are maturely drained, because the streams have had a longer time to evolve into an efficient drainage system compared with the streams flowing in areas covered by younger glacial deposits.

The age of fluvial sediments overlying the youngest glacial till (Radner Member) of the Glasford Formation yield optically stimulated luminescence (OSL) dates that averaged 131,000 BP.

Most of the glacier caves were located near the 1980s lava dome, where hot steam and volcanic gas emissions from hidden fumaroles on the crater floor or lava dome melted holes in the young glacial ice.