[Footnote 10: See Major C. E. Dutton's map of the plateau country in 6th Ann. Rept. U.S. Geol. Survey, pl. xi. His report on "Mount Taylor and the Zuni plateau," of which this map is a part, presents a vivid picture of the plateau country, and his descriptions are so clear and expressive that any attempt to better them must result in failure. The statement of the geologic and topographic features which is incorporated herein is derived directly from Major Dutton's description, much of it being taken bodily.] The plateau country is not a smooth and level region, as its name might imply; it is extremely rugged, and the topographic obstacles to travel are greater than in many wild mountain regions. It is a country of cliffs and canyons, often of considerable magnitude and forming a bar to extended progress in any direction. The surface is generally smooth or slightly undulating and apparently level, but it is composed of a series of platforms or mesas, which are seldom of great extent and generally terminate at the brink of a wall, often of huge dimensions. There are mesas everywhere; it is the mesa country. Although the strata appear to be horizontal, they are slightly tilted. The inclination, although slight, is remarkably persistent, and the thickness of the strata remains almost constant. The beds, therefore, extend from very high altitudes to very low ones, and often the formation which is exposed to view at the summit of an incline is lost to view after a few miles, being covered by some later formation, which in turn is covered by a still later one. Each formation thus appears as a terrace, bounded on one side by a descending cliff carved out of the edges of its own strata and on the other by an ascending cliff carved out of the strata which overlie it. This is the more common form, although isolated mesas, bits of tableland completely engirdled by cliffs, are but little less common. The courses of the margins of the mesas are not regular. The cliffs sometimes maintain an average trend through great distances, but in detail their courses are extremely crooked; they wind in and out, forming alternate alcoves and promontories in the wall, and frequently they are cut through by valleys, which may be either narrow canyons or interspaces 10 or even 20 miles wide.