"Hikers approach Piegan Pass in the Lewis Range in Glacier National Park, Montana, USA. A scenic walking traverse starts from Siyeh Bend over Piegan Pass to Many Glacier, visiting glorious mountains, valleys and lakes over 13 miles (2260 feet up, 3520 feet down). Since 1932, Canada and USA have shared Waterton-Glacier International Peace Park, which UNESCO declared a World Heritage Site (1995) containing two Biosphere Reserves (1976). Rocks in the park are primarily sedimentary layers deposited in shallow seas over 1.6 billion to 800 million years ago. During the tectonic formation of the Rocky Mountains 170 million years ago, the Lewis Overthrust displaced these old rocks over newer Cretaceous age rocks. Glaciers carved spectacular U-shaped valleys and pyramidal peaks as recently as the Last Glacial Maximum (the last ""Ice Age"" 25,000 to 13,000 years ago). Of the 150 glaciers existing in the mid 1800s, only 25 active glaciers remain in the park as of 2010, and all may disappear by 2020, say climate scientists."
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