More than 570 million years ago, Precambrian sand and mud
deposits blanketed the land that would become western Montana,
before the supercontinent of Pangaea broke up into Europe,
Africa, and the Americas. Traces of blue-green algae are the
only fossils found in Precambrian-era rocks, which can still be
seen in western and central Montana, where later movements
forced them to the surface. Glacier National Park  is almost
entirely Precambrian in origin. Toward the end of the Mesozoic
era, tectonic plates were scudding all over the earth. According
to plate-tectonics theory, as the Atlantic Ocean widened, the
North American Plate was shoved into the Pacific Ocean Plate,
which slipped under the western edge of the continent. The crust
of western Montana, then at the leading edge of the continental
plate, crumpled, cracked, and faulted as it rammed into the
Pacific plate. The crust of Montana eventually over-rode the
Pacific plate and was then lifted high above sea level. About 70
million years ago, the Rocky Mou