<P> Further south, the growth of the Rocky Mountains in the United States was probably caused by an unusual subduction, where the Farallon plate dove at a shallow angle below the North American plate . This low angle moved the focus of melting and mountain building much farther inland than the normal 200 to 300 miles (300 to 500 km). It is postulated that the shallow angle of the subducting plate greatly increased the friction and other interactions with the thick continental mass above it . Tremendous thrusts piled sheets of crust on top of each other, building the extraordinarily broad, high Rocky Mountain range . </P> <P> The current southern Rockies were forced upwards through the layers of Pennsylvanian and Permian sedimentary remnants of the Ancestral Rocky Mountains . Such sedimentary remnants were often tilted at steep angles along the flanks of the modern range; they are now visible in many places throughout the Rockies, and are prominently shown along the Dakota Hogback, an early Cretaceous sandstone formation that runs along the eastern flank of the modern Rockies . </P> <P> Immediately after the Laramide orogeny, the Rockies were like Tibet: a high plateau, probably 6,000 metres (20,000 ft) above sea level . In the last 60 million years, erosion stripped away the high rocks, revealing the ancestral rocks beneath, and forming the current landscape of the Rockies . </P> <P> Periods of glaciation occurred from the Pleistocene Epoch (1.8 million--70,000 years ago) to the Holocene Epoch (fewer than 11,000 years ago). These ice ages left their mark on the Rockies, forming extensive glacial landforms, such as U-shaped valleys and cirques . Recent glacial episodes included the Bull Lake Glaciation that began about 150,000 years ago and the Pinedale Glaciation that probably remained at full glaciation until 15,000--20,000 years ago . </P>

What type of climate is found in the rocky mountains