Task: Question Generation
Input (English): Passage: Up until the mid-19th century, long stretches of the Colorado and Green rivers between Wyoming and Nevada remained largely unexplored due to their remote location and dangers of navigation. Because of the dramatic drop in elevation of the two rivers, there were rumors of huge waterfalls and violent rapids, and Native American tales strengthened their credibility. In 1869, one-armed Civil War veteran John Wesley Powell led an expedition from Green River Station in Wyoming, aiming to run the two rivers all the way down to St. Thomas, Nevada, near present-day Hoover Dam. Powell and nine men – none of whom had prior whitewater experience – set out in May. After braving the rapids of the Gates of Lodore, Cataract Canyon and other gorges along the Colorado, the party arrived at the mouth of the Little Colorado River, where Powell noted down arguably the most famous words ever written about the Grand Canyon of the Colorado:
We are now ready to start on our way down the Great Unknown. Our boats, tied to a common stake, are chafing each other, as they are tossed by the fretful river. They ride high and buoyant, for their loads are lighter than we could desire. We have but a month's rations remaining. The flour has been re-sifted through the mosquito net sieve; the spoiled bacon has been dried, and the worst of it boiled; the few pounds of dried apples have been spread in the sun, and re-shrunken to their normal bulk; the sugar has all melted, and gone on its way down the river; but we have a large sack of coffee. The lighting of the boats has this advantage: they will ride the waves better, and we shall have little to carry when we make a portage.
We are three-quarters of a mile in the depths of the earth, and the great river shrinks into insignificance, as it dashes its angry waves against the walls and cliffs, that rise to the world above; they are but puny ripples, and we but pigmies, running up and down the sands, or lost among the boulders.
We have an unknown distance yet to run; an unknown river yet to explore. What falls there are, we know not; what rocks beset the channel, we know not; what walls rise over the river, we know not; Ah, well! we may conjecture many things. The men talk as cheerfully as ever; jests are bandied about freely this morning; but to me the cheer is somber and the jests are ghastly.
Output (English): What were the names of the two rivers that had a dramatic drop in elevation?