It was not therefore because of the rarity of prehistoric dwellings of either type that the cliff villages of the Mesa Verde were conserved as a national park, nor only because they are the best preserved of all North American ruins, but because they disclose a type of this culture in advance of all others. The builders and inhabitants of these dwellings were Indians having physical features common to all American tribes. That their accomplishment differed in degree from that of the shiftless war-making tribes north and east of them, and from that of the cultured and artistic Mayas of Central America, was doubtless due to differences in conditions of living. The struggle for bare existence in the southwest, like that of the habitats of other North American Indians, was intense; but these were agriculturalists and protected by environment. The desert was a handicap, of course, but it offered opportunity in many places for dry farming; the Indian raised his corn. The winters, too, were short. It is only in the southwest that enterprise developed the architecture of stone houses which distinguish pueblo Indians from others in North America. The dwellers in the Mesa Verde were more fortunate even than their fellow pueblo dwellers. The forested mesas, so different from the arid cliffs farther south and west, possessed constant moisture and fertile soil. The grasses lured the deer within capture. The Mancos River provided fish. Above all, the remoteness of these fastness canyons from the trails of raiders and traders and their ease of defense made for long generations of peace. The enterprise innate in the spirit of man did the rest. II The history of the Mesa Verde National Park began with the making of America. All who have travelled in the southwest have seen mesas from the car-window. New Mexico, Arizona, and parts of Colorado and Utah, the region of the pueblos, constitute an elevated plateau largely arid. Many millions of years ago all was submerged in the intercontinental sea; in fact the region was sea many times, for it rose and fell alternately, accumulating thousands of feet of sands and gravels much of which hardened into stone after the slow great uplifting which made it the lofty plateau of to-day. Erosion did its work. For a million years or more the floods of spring have washed down the sands and gravels, and the rivers have carried them into the sea. Thousands of vertical feet have disappeared in this way from the potential altitude of the region. The spring floods are still washing down the sands and gravels, and the canyons, cliffs, and mesas of the desert are disclosed to-day as stages in the eternal levelling. Thus were created the canyons and mesas of the Mesa Verde. Mesa, by the way, is Spanish for table, and verde for green. These, then, are the green tablelands, forest-covered and during the summer grown scantily with grass and richly with flowers.