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Arches National Park Nature and Science

Arches National Park Geology

The forces of nature have acted in concert to create the landscape of Arches, which contains the greatest density of natural arches in the world. Throughout the park, rock layers reveal millions of years of deposition, erosion and other geologic events. These layers continue to shape life in Arches today, as their erosion influences elemental features like soil chemistry and where water flows when it rains. Arches is located in a "high desert," with elevations ranging from 4,085 to 5,653 feet above sea level.

The climate is one of very hot summers, cold winters and very little rainfall. Even on a daily basis, temperatures may fluctuate as much as 50 degrees. The plants and animals in Arches have many adaptations that enable them to survive these conditions. Some species are found only in this area. The diversity of organisms reflects the variety of available habitat, which includes lush riparian areas, ephemeral pools, dry arroyos, mixed grasslands and large expanses of bare rock.

Arches is located in a "high desert," with elevations ranging from 4,085 to 5,653 feet above sea level. The climate is one of very hot summers, cold winters and very little rainfall. Even on a daily basis, temperatures may fluctuate as much as 50 degrees.

The plants and animals in Arches have many adaptations that enable them to survive these conditions. Some species are found only in this area. The diversity of organisms reflects the variety of available habitat, which includes lush riparian areas, ephemeral pools, dry arroyos, mixed grasslands and large expanses of bare rock.


Although Arches may appear harsh and unchanging, the desert ecosystem is continually evolving. Weather, climatic shifts and geologic processes continue to shape this environment as they have for millennia. More recently, human-caused factors such as air, noise and water pollution, as well as introduced species, have had a much greater impact on natural resources world-wide. The undeveloped landscape of Arches provides an ideal place to study how various environmental factors affect desert ecosystems, and predict what changes might be expected in the future.


For thousands of years, observing the night sky has been fundamental to human life and survival. The sky was a major symbol in the natural world of order and cyclic repetition. Studying the skies brought a sense of normalcy to people's lives. Movement of the planets and stars helped farmers determine when to plant and harvest crops and guided ritual and religious observances. Interpretations of the celestial bodies varied widely among cultures, but often the sky was considered the abode of gods, a place humans could never touch. How do we know that sky watching was important to people of the past? Folk stories, myths, elaborate rituals and festivals, dance and costumes, and complex and symbolic architecture survive today.

Astronomers today ask the same questions posed millennia ago by people sitting around a campfire at night. Those people wondered about the meaning of the flickering but eternal stars overhead and the fragile transient life around them. Today we sometimes take the vast wealth of information on the night sky for granted or are amazed by the accomplishments of ancient astronomers. Our complacency or amazement results from our own night blindness, a symptom caused by our brightly lit and building-enclosed world. Even though we no longer need to track celestial events for our daily survival, we still enjoy gazing at the sky's majestic beauty. Yet this simple pleasure is denied to 90 percent of the world's population. Not only is light pollution an aesthetic problem but it also affects our sense of perspective. Most of the world's population can no longer ponder earth's place in the universe because light pollution of the night sky shrinks the visible universe down from millions of light years to a few miles.

One of our most ancient and universal cultural values is threatened and may become extinct. Fortunately, in Arches National Park, we can reenact that thousand-year-old campfire scene. Campers settling in for the night watch the unfolding drama of our galaxy as stars uncloak one by one. Soon the night sky is filled with thousands of glittering jewels, too many to count. Occasionally, a meteor blazes across the sky. The final act is one that may only be viewed by ten percent of the world's inhabitants and is the most majestic and breathtaking of scenes. Spanning the sky like a cloud of light is a region known as the Milky Way. Earthlings peering into this "band of mist" are looking at the center of our galaxy. Yet light pollution from nearby towns has become evident even here in the last few years.

As these towns grow, so grows the amount of light that encroaches on the dark skies of Arches. Advertising and display lighting, building illumination, upward floodlighting and domestic and industrial security lights vanquish the dark into shadowy corners. How do we protect the beauty of our night skies? Should we turn off street lamps and exterior building lights in favor of dark skies and forego private and public safety and security? Does this starry wilderness deserve the same protection afforded to other resources of this national park? To date there is no federal legislation mandating preservation of the night sky. What is the solution? Do we need another federal regulation? Fortunately, with some modifications of lighting sources and forethought about the placement of lighting, the needs of safety and security and dark skies can all be accommodated.

Light pollution is mostly the product of public lighting that goes to waste. In the United States alone, billions of dollars a year in energy costs could be saved by replacing high wattage, unshielded street lamps and exterior lights with well-directed, lower wattage, shielded lights. Shields would allow the same amount of light to be delivered to the ground where it is needed for safety and security. Additionally, less carbon dioxide and other pollutants would be introduced into the atmosphere because power plants would be producing less energy for lighting. Meanwhile, night-sky watching in Arches remains a democratic joy, available to all and open every night from dusk to dawn. Turn out the lights and look to the dark sky for a great and cosmic show.

Natural Features

Throughout Arches, naturally occurring sandstone basins called "potholes" collect rain water and wind-blown sediment, forming tiny ecosystems where a fascinating collection of plants and animals have adapted to life in the desert. Potholes range from a few millimeters to a few meters in depth, and even the smallest potholes may harbor microscopic invertebrates.

To survive in a pothole, organisms must endure extreme fluctuations in several environmental factors. Surface temperatures vary from 140 degrees Fahrenheit in summer to below freezing in winter. As water evaporates, organisms must disperse to larger pools or tolerate dehydration and the drastic physical and chemical changes that accompany it.

The most extreme conditions exist when a pothole is dry. In addition to the wide temperature fluctuations, ultraviolet light from the sun can damage body tissues. Many aquatic organisms are adapted to acquiring oxygen through water and suffer when exposed to air. Pothole organisms have three main ways of dealing with drought.

"Drought escapers" are winged insects, amphibians and invertebrates that breed in potholes but cannot tolerate dehydration (e.g. mosquitoes, adult tadpole and fairy shrimp, spadefoot toads). In some cases, adults live in permanent water sources or on land and travel to temporary pools to mate and lay eggs. If the pool dries out before the young mature, they die. In the case of tadpole, fairy and clam shrimp, adults must lay their drought-tolerant eggs before the pool dries up.

"Drought resistors" (e.g. snails, mites) have a dormant stage resistant to drying out. These animals have a waterproof layer like a shell or exoskeleton that prevents body tissues from losing too much water while a pool is dry. By burrowing, these animals are able to seal themselves in the layers of fine mud that often coat the bottom of potholes and form an impermeable crust.

"Drought tolerators" (e.g. rotifers, tadpole and fairy shrimp eggs) are able to tolerate a loss of up to 92 percent of their total body water. This remarkable process, known as "cryptobiosis," is made even more remarkable by the fact that many cryptobiotic species can be rehydrated and become fully functional in as little as half an hour. Cryptobiosis is accomplished by a command center that remains hydrated while substituting sugar molecules for water throughout the rest of the body. This transfer maintains the structure and elasticity of an organism's cells during long periods of drought, and enables the organism to withstand the climatic extremes of the desert. In fact, brine shrimp have been hatched from cryptobiotic cysts that endured a flight on the outside of a spacecraft. Many tolerators have only one stage in their life cycle (e.g. egg, larva) that can survive desiccation, and will die if a pool dries up during another phase.

Pothole organisms not only have to endure dry spells, but also must evaluate conditions and decide when to break dormancy. Desert precipitation falls at irregular intervals, and once water enters a pothole there is no guarantee that there is enough for an organism to complete its life cycle. Most organisms living in potholes have very short life cycles, as brief as ten days, reducing the time water is required and allowing them to live in the shallow pools. Even vertebrates such as toads, which are found in other environments, display shorter development times when found in potholes.

However, the presence of water may not be the only cue used by eggs and dormant life forms to activate. Oxygen content, temperature, and other physical and chemical factors of the water may be evaluated. Some organisms produce different types of eggs that hatch on different cues; others lay eggs in different areas so that they experience slightly different environmental conditions. The net result is that not all eggs hatch at once and the species has a better chance of survival. After a pothole fills with water, the small ecosystem experiences many other changes. Water temperatures can be very high, while oxygen levels can be very low. As the pool shrinks from evaporation, its salinity increases and the pH changes. Many organisms are capable of surviving wide fluctuations in these factors, but for some these changes are an indication that the time for dormancy is near.


Arches lies near the heart of a desert called the "Colorado Plateau." Deserts form when weather patterns or geographic land forms create an environment where lack of water limits biotic productivity. Water may exist in an unusable form such as ice, or may be absent altogether. There are four basic types of desert: high pressure, rain shadow, interior continental and coastal. High pressure deserts generally form at the middle latitudes (30 degrees) in each hemisphere where warm, dry air masses descend toward the earth's surface. Rain shadow deserts form in localized high pressure zones caused by warm, dry air descending from mountain ranges. The Colorado Plateau is also in the interior of a large continent, far away from significant water sources.


Because of the elevations throughout the region, with a mean of around 3,000 feet and peaks over 12,000 feet above sea level, the Colorado Plateau is also known as a cold or high desert. Though low humidity allows greater penetration of solar radiation, winter air temperatures frequently drop below freezing. In turn, summertime air and especially ground temperatures can reach levels lethal for many organisms. After sunset, the ground rapidly loses heat to the night sky and ambient air temperatures may drop significantly before dawn. Temperature fluctuations of over 40 degrees in a 24-hour period are not uncommon.

Arches receives more precipitation than many other deserts: about 9 inches annually. August is generally the wettest month, as weather systems

Deserts from the southwest bring brief, intense tropical storms. However, precipitation is highly variable both temporally and spatially. During a single storm, one area may receive significantly more or less water than a neighboring spot less than a mile away.

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