Of the climate of the plateau country it has been said that in the large valleys it is "temperate in winter and insufferable in summer; higher up the summers are temperate and the winters barely sufferable." It is as though there were two distinct regions covering the same area, for there are marked differences throughout, except in topographic configuration, between the lowlands and the uplands or high plateaus. The lowlands present an appearance which is barren and desolate in the extreme, although the soil is fertile and under irrigation yields good crops. Vegetation is limited to a scanty growth of grass during a small part of the year, with small areas here and there scantily covered by the prickly greasewood and at intervals by clumps of sagebrush; but even these prefer a higher level, and develop better on the neighboring mesas than in the valleys proper. The arborescent growth consists of sparsely distributed cottonwoods and willows, closely confined to the river bottoms. On intermediate higher levels junipers and cedars appear, often standing so closely together as to seriously impede travel, but they are confined to the tops of mesas and other high ground, the valleys being generally clear or covered with sagebrush. Still higher up yellow pines become abundant and in places spread out into magnificent forests, while in some mountain regions scrub oak, quaking asp, and even spruce trees are abundant. In the mountain regions there is often a reasonable amount of moisture, and some crops, potatoes for example, are grown there without irrigation; but the season is short. In the Tunicha mountains the Navaho raise corn at an altitude of nearly 8,000 feet, but they often lose the crop from drought or from frost. On the intermediate levels and in the lowlands cultivation by modern methods is practically impossible without irrigation, except in a few favored localities, where a crop can be obtained perhaps two years or three years in five. But with a minute knowledge of the climatic conditions, and with methods adapted to meet these conditions, scanty crops can be and are raised by the Indians without irrigation throughout the whole region; but everywhere that water can be applied the product of the soil is increased many fold. Near the center of the plateau country, in the northeastern corner of Arizona, a range of mountains crosses diagonally from northwest to southeast, extending into New Mexico. In the north an irregular cluster of considerable size, separated from the remainder of the range, is called the Carrizo; and the range proper has no less than three names applied to different parts of it. The northern end is known as the Lukachukai, the central part as the Tunicha, and the southern part as the Chuska or Choiskai mountains, all Navaho names. The two former clusters attain an altitude of 9,500 feet; the Tunicha and the Chuska are about 9,000 feet high, the latter having a flat top of considerable area.