On the northeast side of the Little Colorado a great mesa country stretches far to the northward. These mesas are but minor plateaus that are separated by canyons and canyon valleys, and sometimes by 46 CANYONS OF THE COLORADO. low sage plains. They rise from a few hundred to 2,000 or 3,000 feet above the lowlands on which they are founded. The distinction between plateaus and mesas is vague; in fact, in local usage the term mesa is usually applied to all of these tables which do not carry volcanic moun- powell-canyons-23.jpg NECK SIX MILES NORTHEAST OF JUANTAFOYA. tains. The mesas are carved out of platforms of horizontal or nearly horizontal rocks by perennial or intermittent streams, and as the climate is exceedingly arid most of the streams flow only during seasons of rain, and for the greater part of the year they are dry arroyos. Many of the longer channels are dry for long periods. Some of them are opened only by floods that come ten or twenty years apart. The region is also characterized by many buttes. These are plateaus or mesas of still smaller dimensions in horizontal distance, though their altitude may be hundreds or thousands of feet. Like the mesas and plateaus, they sometimes form very conspicuous features of a landscape and are of marvelous beauty by reason of their sculptured escarpments. Below they are often buttressed on a magnificent scale. Softer beds give rise to a vertical structure of buttresses and columns, while the harder strata appear in great horizontal lines, suggesting MESAS AND BUTTES. 47 architectural entablature. Then the strata of which these buttes are composed are of many vivid colors; so color and form unite in producing architectural effects, and the buttes often appear like Cyclopean temples. There is yet one other peculiarity of this landscape deserving mention here. Before the present valleys and canyons were carved and the mesas lifted in relief, the region was one of great volcanic activity. In various places vents were formed and floods of lava poured in sheets over the land. Then for a time volcanic action ceased, and rains and rivers carved out the valleys and left the mesas and mountains standing. These same agencies carried away the lava beds that spread over the lands. But wherever there was a lava vent it was filled with molten matter, which on cooling was harder than the sandstones and marls through which it penetrated. The chimney to the region of fire below was thus filled with a black rock which yielded more 48 powell-canyons-24.jpg A GROUP OF NECKS NEAR MOUNT TAYLOR. slowly to the disintegrating agencies of weather, and so black rocks rise up from mesas on every hand. These are known as volcanic necks, and, being of a somber color, in great contrast with the vividly colored rocks from which they rise and by which they are surrounded, they 48 powell-canyons-25.jpg PANORAMA FROM THE EDGE OF MOUNT TAYLOR MESA. MESAS AND BUTTES. 49