The dinosaur footprints of the Connecticut River Valley would be too far beneath the surface for humans ever to see them were it not for glaciers that covered much of the northern hemisphere from about 20,000 to about 10,000 years ago. Through pushing, plucking, and scraping, glaciers move a tremendous amount of earthen material from one place to another. Glacial action scoured off softer sedimentary rock between the harder basalt and metamorphic ridges along the valley, which exposed the older sandstone layers containing the footprints.