Various tributaries of the Gila have their sources in this escarpment, and before entering the desolate valley below they run in beautiful canyons which they have carved for themselves in the margin of the plateau. Sometimes these canyons are in the sandstones and limestones which constitute the platform of the great elevated region called the San Francisco Plateau. The escarpment is caused by a fault, the great block of the upper side being lifted several thousand feet above the valley region. Through the fissure lavas poured out, and in many places the escarpment is concealed by sheets of lava. The canyons in these lava beds are often of great interest. On the plateau a number of volcanic mountains are found, and black cinder cones are scattered in profusion. Through the forest lands are many beautiful prairies and glades that in midsummer are decked with gorgeous wild flowers. The rains of the region give source to few perennial streams, but intermittent streams have carved deep gorges in the plateau, so that it is divided into many blocks. The upper surface, although forest-clad and covered with beautiful grasses, is almost destitute of water. A few springs are found, but they are far apart, and some of the volcanic craters hold lakelets. The limestone and basaltic rocks sometimes hold pools of water; and where the basins 40 CANYONS OF THE COLORADO. are deep the waters are perennial. Such pools are known as "water pockets." This is the great timber region of Arizona. Not many years ago it was a vast park for elk, deer, and antelope, and bears and mountain lions were abundant. This is the last home of the wild turkey in the powell-canyons-17.jpg WINGATE CLIFF. United States, for they are still found here in great numbers. San Francisco Peak is the highest of these volcanic mountains, and about it are grouped in an irregular way many volcanic cones, one of which presents some remarkable characteristics. A portion of the cone is of bright reddish cinders, while the adjacent rocks are of black basalt. The contrast in the colors is so great that on viewing the mountain from a distance the red cinders seem to be on fire. From this circumstance the cone has been named Sunset Peak. When distant from it ten or twenty miles it is hard to believe that the effect is produced by contrasting colors, for the peak seems to glow with a light of its own. In centuries past the San Francisco Plateau was the home of pueblo-building tribes, and the ruins of their habitations are widely scattered over this elevated region. Thousands of little dwellings are found, usually built of blocks of basalt. In some cases they were clustered in little towns, and three of these deserve further mention. MESAS AND BUTTES. 41