Cedar Breaks, seen 10,000 feet above, is not a canyon, but the slice of a memory of the earth. The high rim of Cedar Breaks National Monument, southwestern Utah, in a single Landsat 9 view opens into a bowl-shaped escarpment where structure is followed by color: bands, fins and gullies laid down, revised by nature as a diagram tens of millions of years.
The color of the amphitheater palette orange, red, white, and gray also does not appear on the surface only. It is related to the manner in which the sediment was transported, modified, eroded and then constantly recrystallized by the water, ice, as well as gravity. What we have is a topography that can be easily read in space due to the way the layers are arranged, and since the work of exposing the layers was done by erosion.
The novel starts with an ancient basin, which was filled with Lake Claron at times. The carbonate-rich muds settled to the bottom and later solidified into lime and associated layers of sedimentary rocks as the cliffs that dominate the cliffs today and formed during the Eocene through the Oligocene some 50 to 25 million years ago. It was repeated in long intervals: sometimes the lake was wetter and deeper; sometimes it became shallow, or even ceased to exist. These changes were chemically important. In the case where muddy sediments were not exposed to much oxygen, iron was not oxidized, and the rocks were formed in lighter colors- white or gray. As the environment became drier, and there was more exposure to oxygen, such minerals that contained iron “rusted”, creating iron-bearing layers of red and orange. The effect of that chemical rhythm is still visible in Cedar Breaks, in the form of a pattern of stripes inscribed in the ground in climate coded features, which can be viewed through ground photography and on a larger scale through satellite photography.
The Landsat 9 can bring more than a pretty view in scenes such as these. The Operational Land Imager and Thermal Infrared Sensor sensors on the satellite gather information over a variety of spectral bands which means that very small variations of surface reflectance and of surface heat can be segmented and contrasted across the land. In 14-bit quantization, Landsat 9 is able to distinguish much finer color changes in darker objects than the earlier generations- this is useful when rock, vegetation, shadow, and moisture are competing within the same frame. The sensitivity would aid in cohering the patterns of the amphitheater at regional scale, which with field observations alone would be even slower and more disjointed.
Deposition was then followed by elevation. Cedar Breaks is located at the highest point of the Grand Staircase, which is a series of sedimentary “steps” that run southwards to the Grand Canyon. Uplift transported these lake-sediments gradually to great altitude, and made the rim some 10,000 feet (3,000 meters) higher than sea-level. The monument is also on a geologic boundary where the processes of extension and faulting affect the form of the landscape; the Hurricane Fault is a major boundary between provinces in southwestern Utah. The uplift and faulting elevated the rocks over long periods of time in a manner that did not just increase their elevation, but promoted the formation of crevices and weaknesses in the rocks which could be exploited by water and ice.
That exploitation is being exhibited in the drainages radiating off the rim. The headwaters of the Ashdown Creek and its tributaries have cut the escarpment and have incised into the Claron Formation and transported the silt downslope. The processes are gradual but relentless: carbonate minerals in limestone can be dissolved in rather weak rain water that is slightly acidic; freeze-thaw cycles can split up cracked joints; gravity can drive loose blocks down off steep walls. Narrow rock walls may over time evolve into fins and fins may be detached into pillars as protective caprock is broken and eroded away.
Another control layer is the high elevation. The cold weather is frequent, and frequent enough, and frost action is a regular thing, and snow may be excessive. “The high elevation influences everything from the weather to the plants and animals that live there. Winters are long, cold, and snowy, with nearby Brian Head seeing 30 feet (10 meters) of snowfall each year on average“. Such climate makes slopes active with seasonal melt and freeze and also limits soil development and thick vegetation cover.
Nevertheless, life continues to exist on the periphery. Some of the Bristlecone pines are more than 1700 years old and they cling to the open limestone rim. Their slower rate of growth produces thick wood, not easy to decay, and their power of surviving in thin and rocky soils puts them in a situation where competition is minimal. As an engineering notion, they constitute living test results of constraint: a species that flourishes in one of the few areas where temperature, wind and substrate permit other plants to form.
The foundation was formed by water and sediment, but the darker punctuations are given by volcanic rocks around the scene. Part of the Markagunt Plateau has had basaltic eruptions in the geologically recent history; the volcanic field there is active between 5.3 million years ago to less than 10,000 years ago. The dark basaltic flows, and tuff-deposits are found above, or beside the sedimentary beds, with an alternative record of material: the lake muds became limestone beneath, the lava- and ash-made rocks above.
Cedar Breaks can be called an amphitheater, but the designation is a way of underrating the reality that remote sensing tells us. It is a diagnostic surface as well, an exposed stratigraphic stack at high altitude, eroded by drainage and enlarged by weathering. The “rainbow” in that regard is no ornament. It is the observable result of the work of chemistry, deposition, tectonics, and erosion working on various time scales and combined into one frame which can be revisited over and over by a satellite.
