On the east these mountains break down rather abruptly into the broad valley of the Chaco river, or the Chaco wash, as it is more commonly designated; on the west they break down gradually, through a series of slopes and mesas, into the Chin Lee valley. Canyon de Chelly has been cut in the western slope by a series of small streams, which, rising near the crest of the mountain, combine near its head and flow in a general westerly direction. The mouth of the canyon is on the eastern border of the Chin Lee valley. It is 60 miles south of the Utah boundary and 25 miles west of that of New Mexico; hence it is 60 miles east and a little north from the old province of Tusayan, the modern Moki, and 85 miles northwest from the old province of Cibola, the modern Zuni. Its position is almost in the heart of the ancient pueblo region; the Chaco ruins lie about 80 miles east, and the ruins of the San Juan from 60 to 80 miles north and northeast. [Illustration: Plate XLII Map of Canyon De Chelly and Its Branches Surveyed by Cosmos Mindeleff] The geographic position of Canyon de Chelly has had an important effect on its history, forming as it does an available resting place in any migratory movement either on the north and south line or east and west. The Tunicha mountains are a serious obstacle to north and south movement at the present day, but less so than the arid valleys which border them. Except at one place, and that place is difficult, it is almost impossible to cross the mountains with a wheeled vehicle, but there are innumerable trails running in all directions, and these trails are in constant use by the Navaho, except in the depths of winter. The mountain route is preferable, however, to the valley roads, where the traveler for several days is without wood, with very little water and forage, and his movements are impeded by deep sand. To the traveler on foot, or even on horseback, Canyon de Chelly is easily accessible from almost any direction. Good trails run northward to the San Juan and northeastward over the Tunicha mountains to the upper part of that river; Fort Defiance is but half a day's journey to the southeast; Tusayan and Zuni are but three days distant to the traveler on foot; the Navaho often ride the distance in a day or a day and a half. The canyon is accessible to wagons, however, only at its mouth. The main canyon, shown on the map (plate XLII) as Canyon de Chelly and known to the Navaho as Tse-gi, is about 20 miles long. It heads near Washington pass, within a few miles of the crest of the mountain, and extends almost due west to the Chin Lee valley. The country descends by a regular slope from an altitude of about 7,500 feet at the foot of the main crest to about 5,200 feet in the Chin Lee valley, 25 miles west, and is so much cut up locally by ravines and washes that it is impassable to wagons, but it preserves throughout its mesa-like character.