After the Rockies emerged from the sea, it took them 10 million years to rise. Sixty million years ago, they reached spectacular heights of 28,000 feet, rivaling the Himalayas today. The deep history of the Rocky Mountains is beginning to take shape.

A weak line in the crust explains why the Rockies rose 500 to 1000 miles inland. Fossil leaves show that the young Rocky Mountains were once nearly twice their size. Half of the rock that formed them originally has vanished. Scientists are now trying to unravel the processes that cut them down to the size they are today.

One hundred million years ago, a vast inland sea covered the area where the American Rockies stand tall today. Seventy million years ago, the sea retreated as the Rockies began to rise. Sixty million years ago, the Rocky Mountains reached their pinnacle, towering into the sky with peaks over 28,000 feet high, rivaling the Himalayas.

Since then, the entire mountain range has lost nearly half its height. Geologists investigating the history of the Rockies are trying to discover what happened to the billions of tons of rock that went missing. The investigation starts with a mystery at the Owl Creek Mountains in the Wyoming Rockies. The Mountains are sliced by a river that has formed a deep canyon.

"Well, the Wind River is very perplexing. It chose to take a straight path right through the core of a major mountain range. This is not the way that rivers normally act. Usually it will take the easiest route which is a downhill. But this river cut right through a major mountain range and has been a mystery. It is a very perplexing issue to early geologists in the region."

This river led to confusion as early as 1806 when Marry Whether Louis and William Clark mapped the area during their famous expedition to explore uncharted territory.

小編有約：哦，本期的聽力中有一個非常著名的“劉易斯與克拉克遠征”，Daisy簡單介紹介紹，劉易斯與克拉克遠征（Lewis and Clark expedition，1804年–1806年）是美國國內首次橫越大陸西抵太平洋沿岸的往返考察活動。領隊為美國陸軍的梅里韋瑟·劉易斯上尉（Meriwether Lewis）和威廉·克拉克少尉（William Clark），該活動是由杰斐遜總統所發起。大家應該猜到，由總統發起的，一定是想奪得這里的土地啦！呵呵~~具體詳情就自己查啰。

課后題目：Daisy想讓大家自己了解了解美國的地理，你能告訴我，文中出現的“ Owl Creek Mountains”在美國哪里嗎？它有什么特征呢？

來源:可可英語 http://www.ccdyzl.cn/Article/201111/159555.shtml