Stories in Stone

Map of Colorado Plateau

Striking geologic features, including stark black lava flows, wind-rippled cinder dunes, rusty red sandstones and vast expanses of multi-hued sedimentary layers dominate the landscapes of Sunset Crater Volcano and Wupatki national monuments. Both monuments are located in a large geographic region known as the Colorado Plateau. Various rock layers, called formations, document how this area has changed through geologic time.

The rock formations and regional geologic events affected both the physical and spiritual world of the people living in the area. Even today, from the quality of your water to where you build your house, geology affects your life in many ways.

Water, Water, Everywhere
The oldest rock layers exposed in the two monuments, the Kaibab and Moenkopi formations, are found at Wupatki. As dry as the sun-baked desert looks today, a closer look at the rocks reveals water-formed ripples, mud cracks, river gravels, and the imprints of thousands of shells from clams, mollusks and other marine life.

Kaibab Formation
The 240 million-year-old Kaibab Formation is made of limestone, a rock type formed on the sea floor. Prior to the uplift of the Colorado Plateau, this region was near sea level and was periodically covered by large inland seas. Like all oceans, the sea covering this area was teeming with billions of microscopic organisms, whose skeletal remains gently floated to the ocean floor after the creatures died. Over millions of years, the tiny skeletons amassed and, mixed with sand and clay, formed a layer of briny ooze hundreds of feet thick. Through time, this ooze compacted and hardened to form limestone.

Moenkopi Formation
Well-preserved ripple patterns, abundant mud cracks and fossilized burrow traces are seen in the layered sandstone and shale of this formation. This deep red, 200 million-year-old rock layer records a period of meandering rivers, tidal flats and other near shore deposits laid down on top of the Kaibab after the seas had retreated westward. A new type of animal was flourishing; dinosaurs, thriving on the moist climate's lush vegetation, were roaming the land. River Gravel Deposits As the Little Colorado River cut down through the sedimentary layers over the last two million years, it left behind gravel deposits that document its ancestral meandering. These deposits form flat-topped caps of grayish gravel over many of the red Moenkopi hills.

diagram - geologic cross-section

An Uplifting Experience
About 80 million years ago, near the Pacific coast, two large pieces of the earth's crust were colliding. The resulting compressive forces caused the western edge of North America to fold and buckle. This compression caused the Colorado Plateau to slowly inch upward, eventually reaching over a mile in height. Though many of the rock layers on the plateau remained level, great folds and faults formed in the process; the Doney fault and Black Point monocline in Wupatki are examples of such features (see above). With the plateau's mass of marine and coastal rocks now exposed to weathering by rain, river and wind, the magnificent canyons and sculptured rock formations characteristic of the Plateau began to develop. Then about 40 million years ago, compression and uplifting ceased. However, the slow, imperceptible erosional processes are still at work today wearing down mesa tops and deepening the canyons. Uplift and buckling of the Colorado Plateau resulted in fracturing of the local rock layers. Water seeped down through the cracks in the Kaibab limestone, dissolving the rock to form long, interconnected vertical fractures. Small surface openings to this fracture system, called blowholes, breathe as the underground air responds to changes in the temperature and pressure of the above ground air. One such blowhole may be seen along the Wupatki Pueblo trail.

Life Among the Rocks
Using the help of rocks deposited by water, fractured by great uplifts and erupted out of volcanoes, the people here carved a life out of the desert. Because of fractures formed during uplift, the sandstone and limestone break naturally along flat edges, making great building blocks. Clay formed from the erosion of rocks made a mortar that held the walls together. Chert found in the river gravel deposits was knapped into arrow points and cutting tools.

What did the ancestral puebloans think of the occasional pyrotechnics? Corn cob impressions found in chunks of basalt indicate that corn may have been given as an offering to the lava. Were they trying to stop the flow? Or honoring it as a blessing? For the Hopi, Sunset Crater is home to the kind and compassionate Kana’a Kachina (Kachinas are the benevolent spirit beings of the Hopi). Some people speculate the black cinders acted as a valuable moisture-holding mulch for crops and may have influenced people to move to the Wupatki area around AD 1100.

Blowholes are also important. Stories among the Hopi refer to these openings as the source of the wind and the home of the wind god, Yaponcha. Wind is significant to the farming Hopi, for it can create clouds which bring needed rain. Many large pueblo sites in northern Arizona, including Wupatki Pueblo, are located near blowholes.

Rocks are no less important to people today. Buildings are built from rock, and icy roads are made safer with cinders and sand. Flakes of volcanic glass (obsidian), sharper than steel blades, are used for eye and heart surgery. The list is long. Think of how your day is made better by rocks...perhaps you'll be surprised.

For more information visit Northern Arizona University's Canyons, Cultures and Environmental Change web site.

Last updated: February 24, 2015

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