[Illustration: The Backbone of the Continent. Photograph by R. H. Chapman, U. S. Geol. Survey.] Four large rivers of immense length took their rise towards the north on the summits of the Backbone, the greatest three springing like triplets of a single mother from practically the same spot in what is now Wyoming. One of these, rushing toward the north-west over a cataract that rivals Niagara, and over falls and wild rapids, swept into the Pacific through a line of dangerous breakers which, notwithstanding the labours of our best engineers, still remains a barrier to the entrance. This was the "River of the West," now the Columbia, taking its name from the ship of Captain Gray, the first to sail into its mouth. Another river, the real continuation of the Mississippi, ran its course for some three thousand miles before joining the parent stream at a point still more than a thousand miles from the Gulf of Mexico, navigable in high-water season for boats of moderate draught for about two thousand miles of its length above the junction. This was the Missouri, at first the main highway from the east into the wilderness, leading the trappers and traders to the very threshold of the great mountains. The third river, the Seedskedee, the Rio Colorado Grande of the Spaniards, now the Green and Colorado, started just over the range at the head of the Missouri and the Columbia, and leaping down the westerly precipices in bold cataracts, made for the south-west and the gulf now called California, never heeding the mountain barriers, but for half its two thousand miles of length cleaving through them, a series of terrifying chasms, deep and difficult, where its waters are torn by hundreds of loud rapids, and whose tributary chasms unite with the mother gorges to interpose almost insurmountable obstacles in the path of the explorer,—the last portion of the wilderness to be vanquished and, though vanquished, yet to this day formidable and defiant. The fourth river, less in magnitude and vigour than the others, but nevertheless fractious, rose some miles southward of their birthplace on the rugged slopes of spurs of the great range, and sweeping to the south and south-east entered the Gulf of Mexico. This was the Rio Grande del Norte, now abbreviated to Rio Grande, and forming for a long distance the boundary of Mexico. It was on this river that the first settlements were made in the wilderness, by Europeans, in what is now New Mexico. [Illustration: Wilderness of the Upper Missouri. Photograph by R. H. Chapman, U. S. Geol. Survey.]