16th.--Crossing the river, here about 400 feet wide, by a very good ford, we continued to descend for seven or eight miles on a pleasant road along the right bank of the stream, of which the islands and shores are handsomely timbered with cottonwood. The refreshing appearance of the broad river, with its timbered shores and green wooded islands, in contrast to its dry and sandy plains, probably obtained for it the name of Green river, which was bestowed on it by the Spaniards who first came into this country to trade some 25 years ago. It was then familiarly known as the Seeds-ke-dee-agie, or Prairie Hen (_tetrao urophasianus_) river; a name which it received from the Crows, to whom its upper waters belong, and on which this bird is still very abundant. By the Shoshonee and Utah Indians, to whom belongs, for a considerable distance below, the country where we were now traveling, it was called the Bitter Root river, from a great abundance in its valley of a plant which affords them one of their favorite roots. Lower down, from Brown's hole to the southward, the river runs through lofty chasms, walled in by precipices of _red_ rock; and even among the wilder tribes which inhabit that portion of its course, I have heard it called by Indian refugees from the California settlements the Rio _Colorado_. We halted to noon at the upper end of a large bottom, near some old houses, which had been a trading post, in lat. 41° 46' 54". At this place the elevation of the river above the sea is 6,230 feet. That of Lewis's fork of the Columbia at Fort Hall is, according to our subsequent observations, 4,500 feet. The descent of each stream is rapid, but that of the Colorado is but little known, and that little derived from vague report. Three hundred miles of its lower part, as it approaches the Gulf of California, is reported to be smooth and tranquil; but its upper part is manifestly broken into many falls and rapids. From many descriptions of trappers, it is probable that in its foaming course among its lofty precipices it presents many scenes of wild grandeur; and though offering many temptations, and often discussed, no trappers have been found bold enough to undertake a voyage which has so certain a prospect of a fatal termination. The Indians have strange stories of beautiful valleys abounding with beaver, shut up among inaccessible walls of rock in the lower course of the river; and to which the neighboring Indians, in their occasional wars with the Spaniards and among themselves, drive their herds of cattle and flocks of sheep, leaving them to pasture in perfect security.