The tracks of the dinosaurs are found in rocks which apparently were formed from river deposits of sands and muds. In other rocks closely associated have been found the bones of dinosaurs, other reptiles, and animals related to the frog or toad. Some of these creatures apparently were “largely if not entirely terrestrial in habit” while others probably lived in either fresh water streams or swamps.
THE PAINTED DESERT
THE ROCKS OF ZION CANYON AND RAINBOW NATURAL BRIDGE
(NAVAJO SANDSTONE; JURASSIC PERIOD)
The lure of a desert with its drifting sands, its scattered oases, and its broad extent has ever been great. Today in the Southwest, cut off from the moist ocean breezes of the west by the lofty Sierra Nevadas and further isolated by the Rocky Mountains to the east, is America’s great desert region. Here the winds and the rains are constantly at work tearing down and sculpturing the great land masses, while in places the wind is piling up the sand and debris to form dunes and new lands.
Far back in history, probably in what is known as the Jurassic Period, southwestern United States witnessed conditions of climate and environment which were perhaps somewhat comparable though probably far more desert-like than those which exist today. The land which had been raised in the preceding period to form a great flood-plain remained above sea level. Lofty mountains were formed to the west and like the Sierras of today, they robbed the east-travelling winds of their moisture. These mountains were very high and furnished a vast supply of sediment which was carried down into the arid basin to the east, worked and reworked by the wind, and finally deposited as a great layer of sand.
ZION CANYON. NAVAJO SANDSTONE
RAINBOW NATURAL BRIDGE. NAVAJO SANDSTONE