Canyonlands National Park

Canyonlands National Park

Geology

Natural Features & Ecosystems

To many, the most outstanding natural features of Canyonlands are the park's geologic formations. In each of the districts, visitors can see the remarkable effects of millions of years of erosion on a landscape of sedimentary rock.

Two unusual natural features are common in Canyonlands and intrigue both scientists and visitors: biological soil crust and ephemeral pools (potholes). Biological soil crust is a living groundcover that forms the foundation of high desert plant life.

Potholes are naturally occurring basins in sandstone that collect rainwater and wind-blown sediment. These potholes harbor organisms that are able to survive long periods of dehydration, and also serve as a breeding ground for many high desert amphibians and insects. Both of these communities are very vulnerable to human impacts.

Environmental Factors

Although Canyonlands 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 Canyonlands provides an ideal place to study how various environmental factors affect desert ecosystems, and predict what changes might be expected in the future.

Geologic Formations

Deposition

Canyonlands National Park is a showcase of geology. In each of the districts, visitors can see the remarkable effects of millions of years of erosion on a landscape of sedimentary rock. For hundreds of millions of years, material was deposited from a variety of sources in what is now Canyonlands National Park. As movements in the earth's crust altered surface features and the North American continent migrated north from the equator, the local environment changed dramatically.

Over time, southeast Utah was flooded by oceans, crisscrossed by rivers, covered by mudflats and buried by sand. The climate has resembled a tropical coast, an interior desert, and everything in between. Layer upon layer of sedimentary rock formed as buried materials were cemented by precipitates in ground water. Each layer contains clues, like patterns or fossils, that reveal its depositional environment. For example, the red and white layers of Cedar Mesa Sandstone occur where floods of iron-rich debris from nearby mountains periodically inundated coastal dunes of white sand. Only a trace of iron is needed to color a rock red.

It is difficult to imagine such major changes and the time scale they spanned. Equally surprising is the fact that all of these rock layers were flat when they were deposited. Only recently, speaking in geologic time, have these layers eroded to form the remarkable landscape seen today.

Erosion

Until about 15 million years ago, most of the canyonlands area was near sea level. Local uplifts and volcanic activity had created features like Capitol Reef's Waterpocket Fold and the La Sal Mountains near Moab, but then movements in the earth's crust caused the whole area to rise. Today, the average elevation is over 5,000 feet above sea level.

The uplifting of this region, known as the Colorado Plateau, marked a shift from a depositional environment to one of erosion. The Colorado and Green rivers began to downcut and are now entrenched in canyons over 2,000 feet deep. Sediment-filled storm run-off drains into these rivers, scouring the surrounding landscape of into a network of tributary canyons, pour-offs and washes.

How sedimentary rock weathers depends largely on its exposure to water. An erosion- resistant caprock of White Rim Sandstone may protect a weaker layer of shale until only a thin spire remains. Examples of such "standing rocks" can be seen in both the Island in the Sky and the Maze districts. In addition to floods, the expansion of freezing water is a powerful erosive force. As ice loosens surface material and widens cracks, everything becomes more vulnerable to the next big storm.

Another significant factor in the shaping of Canyonlands is the Paradox Formation, a layer of sea water evaporates from the Pennsylvanian Period. Deeply buried, the salts in this layer can liquefy under the weight of the overlying rock, flowing, like toothpaste, away from the source of greatest overburden. In response, the upper layers may bow up, creating a salt dome, or erode and collapse, creating a salt valley.

This phenomenon is especially visible in the Needles, where parallel cracks or "joints" formed in the surface rock as buried layers slumped toward Cataract Canyon. These cracks are perpendicular to an older system of cracks created by the "Monument Uplift." The resulting crosshatched pattern of joints has eroded so that great blocks of sandstone have been reduced to thin spires of rock.

Upheaval Dome

Canyonlands is a place of relative geologic order. Layers of sedimentary deposits systematically record chapters in the park's past. With some exceptions, these layers have not been altered, tilted or folded significantly in the millions of years since they were laid down by ancient seas rivers or winds.

Upheaval Dome is quite a different story. In an area approximately three miles (5km) across, rock layers are dramatically deformed. In the center, the rocks are pushed up into a circular structure called a dome, or an anticline. Surrounding this dome is a downwarp in the rock layers called a syncline. What caused these folds at Upheaval Dome? Geologists do not know for sure, but there are two main theories which are hotly debated.

Salt Dome Theory

A thick layer of salt, formed by the evaporation of ancient landlocked seas, underlies much of southeastern Utah and Canyonlands National Park. When under pressure from thousands of feet of overlying rock, the salt can flow plastically, like ice moving at the bottom of a glacier. In addition, salt is less dense than sandstone. As a result, over millions of years salt can flow up through rock layers as a "salt bubble", rising to the surface and creating salt domes that deform the surrounding rock.

When geologists first suggested that Upheaval Dome was the result of a salt dome, they believed the land form resulted from erosion of the rock layers above the dome itself. Recent research suggests that a salt bubble as well as the overlying rock have been entirely removed by erosion and the present surface of Upheaval Dome is the pinched off stem below the missing bubble. If true, Upheaval Dome would earn the distinction of being the most deeply eroded salt structure on earth.

Impact Crater Theory

When meteorites collide with the earth, they leave impact craters like the well-known one in Arizona. Some geologists estimate that roughly 60 million years ago, a meteorite with a diameter of approximately one-third of a mile hit at what is now the Upheaval Dome. The impact created a large explosion, sending dust and debris high into the atmosphere. The impact initially created an unstable crater that partially collapsed. As the area around Upheaval Dome reached an equilibrium, the rocks underground heaved upward to fill the void left by the impact. Erosion since the impact has washed away any meteorite debris, and now provides a glimpse into the interior of the impact crater, exposing rock layers once buried thousands of feet underground.

Upheaval Dome Today

Whatever the origin of Upheaval Dome, it is the result of erosion of a structural dome. Rock layers now at the surface within the dome were once buried at least a mile underground and are not visible anywhere else in the nearby area. While some call this feature a crater, it is not a crater in the traditional sense of the word, but simply another example of the erosion which created Canyonlands National Park.

Biological Soil Crust

Biological soil crust is a living groundcover that forms the foundation of high desert plant life in Canyonlands and the surrounding area. This knobby, black crust is dominated by cyanobacteria, but also includes lichens, mosses, green algae, microfungi and bacteria.

Cyanobacteria, previously called blue-green algae, are one of the oldest known life forms. It is thought that these organisms were among the first land colonizers of the earth's early land masses, and played an integral role in the formation and stabilization of the earth's early soils. Extremely thick mats of these organisms converted the earth's original carbon dioxide-rich atmosphere into one rich in oxygen and capable of sustaining life.

When wet, Cyanobacteria move through the soil and bind rock or soil particles, forming an intricate web of fibers. In this way, loose soil particles are joined together, and an otherwise unstable surface becomes very resistant to both wind and water erosion. The soil-binding action is not dependent on the presence of living filaments. Layers of abandoned sheaths, built up over long periods of time, can still be found clinging tenaciously to soil particles, providing cohesion and stability in sandy soils at depths up to 10cm.

Nitrogen fixation is another significant capability of cyanobacteria. Vascular plants are unable to utilize nitrogen as it occurs in the atmosphere. Cyanobacteria are able to convert atmospheric nitrogen to a form plants can use. This is especially important in desert ecosystems, where nitrogen levels are low and often limiting to plant productivity.

Soil crusts have other functions as well, including an ability to intercept and store water, nutrients and organic matter that might otherwise be unavailable to plants.

Unfortunately, many human activities negatively affect the presence and health of soil crusts. Compressional stresses placed on them by footprints or machinery are extremely harmful, especially when the crusts are dry and brittle. Tracks in continuous strips, such as those produced by vehicles or bicycles, create areas that are highly vulnerable to wind and water erosion. Rainfall carries away loose material, often creating channels along these tracks, especially on slopes.

Impacted areas may never fully recover. Under the best circumstances, a thin veneer of cryptobiotic soil may return in five to seven years. Damage done to the sheath material, and the accompanying loss of soil nutrients, is repaired slowly during up to 50 years of cyanobacterial growth. Lichens and mosses may take even longer to recover.

Avoiding these fragile crusts is simple. Always drive or ride on designated roads. Respect road closures and search for places wide enough to pass other vehicles rather than driving over roadside vegetation. When hiking, always walk on marked trails, or on other durable surfaces such as rock or in sandy washes.

Deserts

Canyonlands forms the heart of a "high" or "cold" desert called the Colorado Plateau. The arid climate of this area is caused by many factors.

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.

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

Rivers

The Colorado and Green rivers wind through the heart of Canyonlands, cutting through layered sandstone to form two deep canyons. Both rivers are calm upstream of the Confluence, ideal for canoes, kayaks and other shallow water craft. Below the Confluence, the combined flow of both rivers spills down Cataract Canyon with remarkable speed and power, creating a world-class stretch of white water.

Flows

River flows are dependent upon snowmelt and rainfall. The character of the rivers changes dramatically depending on the season. High water generally stretches from early May to late June. Recorded river flows are available from the US Geological Survey, or by calling (801) 539-1311. Snowmelt peak flow forecasts are available from the Colorado Basin River Forecast Center.

Launch/Take Out Options

On both rivers, all launch ramps are outside Canyonlands. Launch locations on the Green River typically include Green River State Park, Ruby Ranch or Mineral Bottom. On the Colorado, boaters typically use the Potash or Moab ramps.

There is no vehicle access to the rivers near the Confluence or in Cataract Canyon. While hiking trails lead to the rivers from each of the districts, these trails are too long and rugged to be seriously considered for shuttles, even for inflatables and other lightweight boats. Groups wishing to avoid the white water must arrange upstream travel back to Moab. This shuttle is handled by two jet boat operators in Moab:

Tex's Riverways: (877) 662-2839 or (435) 259-5101
Tag-A-Long Expeditions: (435) 259-8946

Ephemeral Pools

Throughout Canyonlands, naturally occurring sandstone basins called emphemeral pools or "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 bodily 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 bodily 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 more unique 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.

A pothole is a unique habitat that is very easily disturbed. Pothole organisms are sensitive to sudden water chemistry changes, temperature changes, sediment input, being stepped on, and being splashed out onto dry land. Human use of pothole water by swimming, bathing or drinking may change the salinity or pH of a pool drastically. More importantly, this change occurs suddenly, unlike the slow, natural changes to which organisms can adapt. Hikers should therefore avoid using water in potholes as well as walking through dry ones.

While these tiny ecosystems may seem unimportant, they can act as an indicator for the health of the larger ecosystems in which they occur. These pools do not have the ability to counteract acids, so the acid rain caused by industrial pollution may be lethal. Pothole health is monitored in Canyonlands in order to track significant changes in our environment.

Rivers & Streams

Among the natural communities of plants and animals existing in the high desert ecosystem, none is as lush or rich in animal life as the riparian community. Riparian zones are the lush belts of vegetation found along rivers and intermittent streams (which disappear underground periodically along their course). The Colorado River flows through Canyonlands, and one of its major tributaries, the Green River, joins it inside the park at the Confluence. Intermittent streams are found in Horseshoe, Salt Creek and other canyons in the park.

The plants in riparian zones are not adapted to the low-water conditions existing in the surrounding desert. A few of the common shrubs and trees that grow in the lower elevation riparian zones of southeastern Utah are Fremont cottonwood, a few species of willows, seepwillow, tamarisk, water birch, Russian olive, and boxelder.

Wildlife is abundant in riparian zones for a simple reason: all animals need water to survive. Even many desert-dwelling creatures must visit open water sources to drink. Desert bighorn sheep can go for days without drinking, but must eventually find a stream, spring or pothole. Large mammals like mule deer and mountain lions may have huge territories, but must drink at various intervals. Besides using riparian zones as water sources, predators find prey more abundant here.

Some creatures are adapted to live their whole lives in riparian zones adjacent to water, or in the water itself. Beavers are common along the rivers in Canyonlands. Since these waterways are too large to dam, they live in dens in the riverbanks. Muskrats are also common, and a few river otter live along the Colorado River. Ringtails, raccoons, and skunks are most commonly found along streams.

Many insects are confined to water for all or some stage of their lives. Aquatic insects occupy a variety of microhabitats within streams and ponds. Water striders skim the water surface. Caddis fly larvae, in twig- or sand grain-cases, leave trails in the mud as they slowly move across the stream bottom. Black fly larvae use special attachments, like suction cups, to anchor themselves to rocks in waterfalls, filtering smaller organisms from the flow. Some types of mayfly nymphs hold tight to the bottom of loose cobbles sitting on stream bottoms. Diving beetles and water boatmen are more active swimmers.

Riparian zones are rich in bird life. Most songbirds rely on insects for all or part of their diet, especially during nesting season when their protein needs are highest. Larger water birds, including great blue herons, ducks and Canada geese, feed on aquatic plants or prey on aquatic organisms. Osprey and bald eagles primarily eat fish. Peregrine falcons frequently nest on cliffs along the Green and Colorado, and prey on the songbirds and ducks.

If streams were straight chutes with constant downhill drops, flow would have a constant speed and direction. But streams have irregular sides and bottoms, and are steeper in some places than others, so flow varies. Rocks or curves can create backward flow areas behind them called eddies. Rocks mid-stream with water flowing over the top can create holes, where water rushes forward to fill the void behind the obstruction.

Rapids are created when a large amount of rock washes or falls into a river, constricting the flow. Below the Confluence, the Colorado River enters Cataract Canyon, fourteen miles of dangerous white water that, at peak flows, may produce standing waves over twenty feet high. Flow affects the organisms living in the stream, and also affects humans on river trips. Gaining an understanding of flow, called reading the water, is a fascinating and important part of learning to row or paddle a boat.

Grabens

The grabens in the Needles District of Canyonlands National Park are a system of linear collapsed valleys caused by the movement of underlying salt layers toward the Colorado River canyon. The grabens begin near the Confluence of the Green and Colorado rivers and run roughly parallel to Cataract Canyon for 25 km, veering slightly west before they end. Graben is a German word meaning ditch or grave. In the geologic sense it is a collapsed or down-dropped block of rock that is bordered on its long sides by faults. Grabens are normally associated with "horsts," which are the up-thrown blocks of rock. In German, Horst means aerie, referring to the high nesting sites of predatory birds.

Geologic Processes

The processes that led to the development of the grabens began approximately 300 million years ago in the Pennsylvanian period with the deposition of evaporates (salts) in a shallow inland sea. These deposits, known as the Paradox member of the Hermosa Formation, were later covered by the limestone layers of the upper Hermosa and Rico formations. In the Needles District, the Paradox layer can be 3,000 to 5,000 feet thick.

Sea levels eventually dropped, and white sands blew in from the west, forming large sand dunes. At the same time, red mud and silt was deposited by rain and snow melt from the Uncompahgre Mountain to the east. The resulting red and white beds alternated, forming the lower beds of the Cutler Formation, or the Cedar Mesa Sandstone that is dominant in the Needles District today.

Sediment from a variety of environments continued to accumulate on top of these layers for millions of years. Approximately 60 million years ago, a tectonic plate collision called the Laramide Orogeny created the Rocky Mountains. Shortly after, a regional upwarp called the Monument Uplift caused the sedimentary layers in the Needles to tilt gradually westward. This event also formed joints, or long parallel fractures in the rock, throughout the Needles. In the vicinity of the grabens there are two joint sets: one trending roughly northeast to southwest, and one trending northwest to southeast. Some of these joints became the faults that border the grabens.

Around 10 million years ago, the uplift of the Colorado Plateau gave rise to the Colorado River and its tributaries. As the Colorado river cut its way downward through the rock layers, it carried away millions of tons of sediment towards the Pacific Ocean.

Necessary Ingredients

Finally, about 55,000 years ago, the ingredients were in place and the grabens began to form. Four factors have been identified as critical to the formation of grabens:

The grabens are a very young geologic feature. Graben growth is thought to be a slow process where small, seismically undetectable movement occurs: as little as one inch per year. The grabens continue to drop and slide toward the river today, and are a fascinating feature of the Needles District.

Desert Varnish

Desert varnish is the thin red to black coating found on exposed rock surfaces in arid regions. Varnish is composed of clay minerals, oxides and hydroxides of manganese and/or iron, as well as other particles such as sand grains and trace elements. The distinctive elements are Manganese (Mn) and Iron (Fe).

The color of rock varnish depends on the relative amounts of manganese and iron in it: manganese-rich varnishes are black; manganese-poor, iron-rich varnishes are red to orange; those intermediate in composition are usually a shade of brown. Varnish surfaces tend to be shiny when the varnish is smooth and rich in manganese.

Desert varnish consists of clays and other particles cemented to rock surfaces by manganese emplaced and oxidized by bacteria living there. It is produced by the physiological activities of microorganisms which are able to take manganese out of the environment, then oxidize and emplace it onto rock surfaces. These microorganisms live on most rock surfaces and may be able to use both organic and inorganic nutrition sources. These manganese-oxidizing microorganisms thrive in deserts and appear to fill an environmental niche unfit for faster growing organisms which feed only on organic materials.

The sources for desert varnish components come from outside the rock, most likely from atmospheric dust and surface runoff. Streaks of black varnish often occur where water cascades over cliffs. No major varnish characteristics are caused by wind.

Thousands of years are required to form a complete coat of manganese-rich desert varnish so it is rarely found on easily eroded surfaces. A change to more acidic conditions (such as acid rain) can erode rock varnish. In addition, lichens are involved in the chemical erosion of rock varnish.

Fossils

BY LEN EISENBERG

185 million years ago, during the age of dinosaurs known as the early Jurassic, Utah was a very different place. Instead of rocky deserts, isolated mountains and deep canyons, sand dunes covered the state from end to end. During rainy periods, lakes formed in low areas between the dunes, and life flourished in them.

Today that great pile of sand is known as the Navajo Sandstone. It forms the cliff walls of Zion National Park, the petrified dunes of Arches National Park, and mesa tops at the Island in Sky and Horseshoe Canyon districts of Canyonlands. In fact, one of the lakes is preserved at Horseshoe Canyon, revealing evidence of a fascinating ecosystem. If we could travel back in time to this lake, what might we see?

Returning to the early Jurassic, we find a sea of sand dunes stabilized by a living carpet of dwarf fern and cryptobiotic soil. From above, the distant glint of silver and gold from a reflected Jurassic sun announces the presence of a chain of lakes. The nearest lake is a few hundred yards wide and nearly a mile long. The lakeshore is lined with stands of conifers and cycads amid meadows of ferns and horsetails. Some of the trees are a foot in diameter and 30 feet high.

Walking on the dunes, the thin crust of vegetation easily breaks apart under our feet. It probably wouldn't take much of a climate shift to dry up the vegetation, the lakes, and set the dunes in motion. It is a sweaty 100 degrees out and a swim sounds good. As we wade into the lake, a group of shrimp-like forms hurry deeper into the water. Some of them have translucent hinged shells on their backs. Vegetated dunes rise above the trees and meadows back from the lakeshore. On one of the dunes a squat, dog-sized reptile is clawing swipes of sand out of a hole. Its short, strong arms have no trouble digging deep into the dune and uncovering a nest of wasp larvae. The creature licks up the larvae, and its thick, bristly hide protects it from the angry parents.

On the northern side of the lake, microscopic organisms deposit mats of limy sediment on the lake bottom, which is marked by winding trails of bottom-mining worms and snails. In places, these mats have built up into large microbial mounds. It appears that if the lake level were to rise, the living surface of the mound would keep pace by growing larger. We notice that all of the mounds and most of the mats are on the south-facing side of the lake, where these photosynthesizing organisms receive the most sun.

Beyond the mounds we see three-toed dinosaurs walking around, each about the size of a skinny turkey. They could be a group of Segisaurus. One scratches the sand with a toe, then quickly thrusts down its narrow jaws and comes up with a mouthful of sand and a wriggling crustacean. We wade closer to get a better look, but they suddenly raise their heads in unison and bolt. We stand in the shallows amid the horsetails, impressed at how fast they can move.Now a hand-sized green and gold dragonfly hovers a few feet away. It chases a flying bug, but then a young pterosaur, a flying reptile, flashes down and snatches the dragonfly from the air. As it flies away, gulping down its meal, we see that the pterosaur has the wingspan of a raven and a long stiff tail that ends in a wedge-shaped web of skin.

Eventually, we arrive offshore of the main area of meadows and trees. In and out of the shadows we see head-high dinosaurs moving-possibly a group of Ammosaurus. Some are on all fours pulling at ferns; others rise up on thick hind legs to reach the tops of plants. There are two or three larger individuals and a similar number of smaller ones, probably adults and offspring. While several make their way to the shoreline for a drink, one or more of the adults watch for danger. In the Jurassic world, it is not long in coming.

A large, meat-eating theropod makes a charge from the trees. The herbivores spin and rush along the shore, galloping on all fours. The predator has the angle and plows into the group, snatching at the smallest. It is butted off by the largest adult who turns in confrontation and blows a braying honk at its foe. The meat-eater is too small to take on this heavy, enraged animal and dodges around it to pursue the rest of the herd. The adult rushes after, braying and honking. The animals soon disappear from view without any sign of slowing. Whew! Not wanting to push our luck, we swim back to our starting place and return to the present.

The Jurassic lake at Horseshoe Canyon is located just east and north of the west side trailhead parking lot (see the bulletin boards for more information). Fossilized wood, microbial mounds, other plant remains, as well as dinosaur and invertebrate tracks have been found there or in nearby areas. Skeletal remains are very rare in the Navajo Sandstone and none have been found at Horseshoe Canyon.

Len Eisenberg is an independent geologist living in Oregon. His main research interest is the Navajo Sandstone, especially the indicators of unusual habitats and events in it.