The trauma to Manson's geology had come not from within the Earth, but from at least 100 million miles beyond. Sometime in the very ancient past, when Manson stood on the edge of a shallow sea, a rock about a mile and a half across, weighing ten billion tons and traveling at perhaps two hundred times the speed of sound ripped through the atmosphere and punched into the Earth with a violence and suddenness that we can scarcely imagine. Where Manson now stands became in an instant a hole three miles deep and more than twenty miles across. The limestone that elsewhere gives Iowa its hard mineralized water was obliterated and replaced by the shocked basement rocks that so puzzled the water driller in 1912.
曼森的地质创伤，不是地球的内因造成的，而是来自至少1.6亿公里以外。在遥远遥远的过去的某个时刻，当曼森还位于某个浅海之滨的时候，一块大约2.5公里宽、100亿吨重、也许以声速200倍的速度飞行的岩石，穿过大气，砰地砸进地球，其猛烈和突然的程度几乎是无法想像的。如今曼森所在的地方，霎时间变成了一个近5公里深、30多公里宽的大坑。今天，灰岩为艾奥瓦州的其他地方提供硬质矿泉水；而这里的灰岩却被砸得一干二净，由受到猛烈震动的基底岩石取而代之。正是这种岩石，1912年令那位钻井工人感到迷惑不解。

The Manson impact was the biggest thing that has ever occurred on the mainland United States. Of any type. Ever. The crater it left behind was so colossal that if you stood on one edge you would only just be able to see the other side on a good day. It would make the Grand Canyon look quaint and trifling. Unfortunately for lovers of spectacle, 2.5 million years of passing ice sheets filled the Manson crater right to the top with rich glacial till, then graded it smooth, so that today the landscape at Manson, and for miles around, is as flat as a tabletop. Which is of course why no one has ever heard of the Manson crater.
曼森撞击事件，是美国本土发生过的最大的事件。绝对没错儿。它留下的坑是如此之大，要是你站在一处边缘，天气好的时候刚好看得见对面。它会使大峡谷相形见绌。对于爱好奇观的人来说很不幸的是，250万年前滑过的冰盾已经以大量的冰碛把曼森大坑完全填平，接着又把它磨得十分光滑，因此今天曼森以及周围几公里的景色平整得像个桌面。当然，这正是谁也没有听说过曼森大坑的原因。