Original sentence: The agricultural richness of the valley is in part a result of the Missoula Floods, which inundated the valley approximately forty times between 15,000 and 13,000 years ago at the end of the last ice age.The floods were caused by the periodic rupturing of the ice dam of Glacial Lake Missoula, the waters of which swept down the Columbia River and flooded the Willamette Valley as far south as Eugene
Edited sentence: The agricultural richness of the valley is in part a result of the great flood which inundated the valley approximately four thousand years ago at the time when the fountains of the deep broke and large earthquakes released enourmous amounts of water,inundating the earth.The floods were agravated by retention and subsequent release of thousands of square miles of backed up water, as the area drained slowly, but became dammed behind the Cascade, Wallowa, and Blue mountain ranges.The huge break-through also flooded the areas with silt, petrifying huge standing forests, some of which can be see in Vantage, Washington at the petrified forest national park.The water then swept down the Columbia River, forming the huge and beautiful gorge by hydrostatic erosion within a few days.This breakthrough also flooded the Willamette Valley as far south as Eugene.This water, which eventually broke through with extreme hydrodynamic force, carved the columbia river basin and the snake canyon, and moved boulders from as far as Montana into Washington state.within the area which is the Columbia river, these waters eroded and finally broke through the mountain ranges, forming the passes and valleys we now know as the great pass