The region may be roughly characterized as a vast sandy plain, arid in the extreme; or rather as two such plains, separated by a chain of mountains running northwest and southeast. In the southern part of the reservation this mountain range is known as the Choiskai mountains, and here the top is flat and mesa-like in character, dotted with little lakes and covered with giant pines, which in the summer give it a park-like aspect. The general elevation of this plateau is a little less than 9,000 feet above the sea and about 3,000 feet above the valleys or plains east and west of it.
The continuation of the range to the northwest, separated from the Choiskai only by a high pass, closed in winter by deep snow, is known as the Tunicha mountains. The summit here is a sharp ridge with pronounced slopes and is from 9,000 to 9,400 feet high. On the west there are numerous small streams, which, rising near the summit, course down the steep slopes and finally discharge through Canyon Chelly into the great Chinlee valley, which is the western of the two valleys referred to above. The eastern slope is more pronounced than the western, and its streams are so small and insignificant that they are hardly worthy of mention.
Still farther to the northwest, and not separated from the Tunicha except by a drawing in or narrowing of the mountain mass, with no depression of the summit, is another part of the same range, which bears a separate name. It is known as the Lukachukai mountains. Here something of the range character is lost, and the uplift becomes a confused mass, a single great pile, with a maximum altitude of over 9,400 feet.
Northwest of this point the range breaks down into Chinlee valley, but directly to the north is another uplift, called the Carriso mountains. It is a single mass, separated from the range proper by a comparatively low area of less than 7,000 feet altitude, while the Carriso itself is over 9,400 feet above the sea.
The western and northwestern parts of the reservation might also be classed as mountainous. Here there is a great mesa or elevated table-land, cut and gashed by innumerable canyons and gorges, and with a general elevation of 7,500 to 8,000 feet. Throughout nearly its whole extent it is impassable to wagons.