How to Claim Your Find:
First you MUST answer all of the following questions via email within 48 hours of your posted log. Any missing answers will disqualify your find. Please do not post your answers in your log. This will also disqualify your find. In either case your log will be deleted.
Go to the coordinates listed at the top of the page and answer the following questions:
Send an email to me with the first line reading GC5JFXC Elephant Arch. Include how many in your party and their caching names.
1. Observing the arch from this location, and based on the information on this page, in your opinion please tell me what type of erosion created this arch?
2. After visiting the location observing the surrounding rock and using the information below please tell me what rock layer the arch is formed in. What led you to this conclusion?
Post A PIC WITH YOUR LOG
As of June 10th, 2019 GC HQ updated the requirements for logging an EarthCache to allow the CO to request the visitor to "…provide a photo of themselves or a personal item to prove they visited the site. A personal item must be an option for those who do not want to photograph themselves. This task is acceptable only as an addition to well-developed logging tasks, not as a substitution."
So as of 06/10/19 "all" logs MUST have a pic attached with either the cacher (or group of cachers) prominently in it OR a personal item (GPS/printed icon/etc.) I will not accept cell phones as a personal item because 1) you more than likely would be using it for the pic 2) Cell phone, in my opinion, is too generic for a "personal item."If you post a group pic you MUST list the cachers names in you log.
Faliure to follow this or any part of the logging tasks will result in disqualification and your log will be "deleted!"
Natural arch
From Wikipedia, the free encyclopedia!
A natural arch, natural bridge or, less commonly, a rock arch is a natural rock formation where a rock arch forms, with an opening underneath. Most natural arches form as a narrow bridge, walled by cliffs, become narrower from erosion, with a softer rock stratum under the cliff-forming stratum gradually eroding out until the rock shelters thus formed meet underneath the ridge, thus forming the arch. Natural arches commonly form where cliffs are subject to erosion from the sea, rivers or weathering (subaerial processes); the processes "find" weaknesses in rocks and work on them, making them larger until they break through. The choice between bridge and arch is somewhat arbitrary. The Natural Arch and Bridge Society identifies a bridge as a subtype of arch that is primarily water-formed. By contrast, the Dictionary of Geological Terms defines a natural bridge as a "natural arch that spans a valley of erosion." The largest natural arch, by a significant margin, is the Xianren Bridge in China, with a span of 122 ± 5 meters (400 ± 15 ft).!
Weather-eroded arches!
Weather-eroded arches begin their formation as deep cracks which penetrate into a sandstone layer. Erosion occurring within the cracks wears away exposed rock layers and enlarges the surface cracks isolating narrow sandstone walls which are called fins. Alternating frosts and thawing cause crumbling and flaking of the porous sandstone and eventually cut through some of the fins. The resulting holes become enlarged to arch proportions by rockfalls and weathering. The arches eventually collapse leaving only buttresses that in time will erode. Many weather-eroded arches are located in Arches National Park, Canyonlands National Park and Grand Staircase-Escalante National Monument which are all located in southern Utah, United States.
Water-eroded arches
Some natural bridges may look like arches, but they form in the path of streams that wear away and penetrate the rock. Pothole arches form by chemical weathering as water collects in natural depressions and eventually cuts through to the layer below.
Natural Bridges National Monument in Utah protects the area surrounding three large natural bridges all of which were formed by streams running through canyons. The largest of which is named Sipapu Bridge with a span of 225 feet (69 m). The Rainbow Bridge National Monument's namesake was also formed by flowing water which created the largest known natural bridge in the Western Hemisphere with a span of 234 feet (71 m), based on a laser measurement made in 2007. Xianren Bridge, also known as Fairy Bridge, in Guangxi, China is currently the world's largest known natural bridge with a span recorded at 400 feet (120 m) by the Natural Arch and Bridge Society in October 2010, with a precision of ±15 feet (4.6 m).
The hike to this cache is a 2 mile (4 mile round trip) hike that takes you along packed double track, loose sand and deep sand in the Bone Wash and along parts of Elephant Arch trail. We were able to do the hike with a range of age in the group in 3 hours. The trail to the arch might continue past the location of this Earthcache but no trail was not discernible and based on the requirements of the reserve we ventured no further.
Deposition of sediments
Kaibab Limestone (Upper Permian)
In later Permian time, the Toroweap Basin was invaded by the warm, shallow edge of the vast Panthalassa ocean in what local geologists call the Kaibab Sea. At that time, Utah and Wyoming were near the equator on the western margin of the supercontinent Pangaea.
Starting 260 million years ago, the yellowish-gray limestone of the fossil-rich Kaibab Limestone was laid down as a limy ooze in a tropical climate. During this time, sponges, such as Actinocoelia meandrina, proliferated, only to be buried in lime mud and their internal silica needles (spicules) dissolved and recrystallized to form discontinuous layers of light-colored chert. This formation can be found in the Hurricane Cliffs above the Kolob Canyons Visitor Center and in an escarpment along Interstate 15 as it skirts the park. This is the same formation that rims the Grand Canyon to the south.
Farther to the west, a complex island arc assemblage formed above a subduction zone. To the east, in western Colorado, a mountain range similar to today's Himalayas called the Uncompahgre Mountains bordered the Utah lowland. The interfingering of the Kaibab with the White Rim Sandstone, now exposed in Capitol Reef National Park area, to the east suggests that the marine facies of the Kaibab migrated eastward in response to a relative sea-level rise, or transgression (the White Rim is not exposed in the Zion area). The sea moved back and forth across Utah, but by the Middle Permian, the sea had withdrawn and the Kaibab Limestone was exposed to erosion, creating karst topography and channels reaching 30 m (100 ft) in depth.
Moenkopi Formation (Lower Triassic)
Volcanoes continued to erupt through the Early Triassic on the north–south trending island arc to the west, which was located along what is now the border between California and Nevada. Shallow, marine water stretched from eastern Utah to eastern Nevada over a beveled continental shelf. As the sea withdrew around 230 million years ago, fluvial, mudflat, sabkha, and shallow marine environments developed, depositing gypsum (from lagoon evaporites), mudstones, limestones, sandstones, shales, and siltstones.
It took many thousands of thin layers of these sediments to form the 1,800-foot (550 m) thick Moenkopi Formation. A prograding shoreline laid down muddy delta sediments which mixed with limy marine deposits. The fossilized plants and animals in the Moenkopi are evidence of a climate shift to a warm tropical setting that may have experienced monsoonal, wet-dry conditions.
The Red Canyon Conglomerate, the basal member of the Moenkopi, fills broad east-flowing paleochannels carved into the Kaibab Limestone. Some of these channels are up to several tens of feet deep and may reach 200 ft (61 m) deep in the St. George area. A thin, poorly developed soil, or regolith, formed over the paleotopographic high areas between the channels.
The depositional environment was a nearshore one where the seashore alternated between advance (transgression) and retreat (regression). The limestones and fossils of the Timpoweap, Virgin Limestone, and Shnabkaib members of the Moenkopi Formation document transgressive episodes. Unlike the Timpoweap and Virgin Limestone members, the Shnabkaib contains abundant gypsum and interbedded mudstone resulting from deposition in a restricted marine environment with complex watertable fluctuations. Regressive, red bed layers separate the transgressive strata. Ripple marks, mud cracks, and thinly laminated bedding suggest that these intervening red shale and siltstone units were deposited in tidal flat and coastalplain environments.
Outcrops of this brightly colored red, brown, and pink banded formation can be seen in the Kolob Canyons and in buttes on either side of State Route 9 between Rockville. Progressively higher beds are exposed until the top of the formation is reached at the mouth of Parunweap Canyon (when traveling to Zions National Park on Route 9).
Chinle Formation (Upper Triassic)
Later, uplift exposed the Moenkopi Formation to erosion and Utah became part of a large interior basin drained by north and northwest-flowing rivers in the Upper Triassic. Shallow river deposition along with volcanic ash eventually became the mineral-rich Chinle Formation. The irregular contact zone, or unconformity, between the Chinle and the underlying Moenkopi can be seen between Rockville and Grafton in southwestern Utah.
Petrified wood and fossils of animals adapted to swampy environments, such as phytosaurs, lungfish, and lacustrine bivalves, have been found in this formation as well as conifer trees, cycads, ferns, and horsetails. Relatively plentiful uranium ore, such as carnotite and other uranium-bearing minerals, has also been found. The purple, pink, blue, white, yellow, gray, and red colored Chinle also contains shale, gypsum, limestone, sandstone, and quartz. Iron, manganese oxides and copper sulfide are often found filling gaps between pebbles. Purplish slopes made of the Chinle can be seen above the town of Rockville.
The sand, gravel, and petrified wood which made up these deposits were later strongly cemented by dissolved silica (probably from volcanic ash from the west) in groundwater. Much of the bright coloration of the Chinle is due to soil formation during the Late Triassic. The lowermost member of the Chinle, the Shinarump, consists of a white, gray, and brown conglomerate made of coarse sandstone, and thin lenses of sandy mudstone, along with plentiful petrified wood. The Shinarump was laid down in braided streams that flowed through valleys eroded into the underlying Moenkopi Formation. This member of the Chinle forms prominent cliffs with thickness up to 200 feet (60 m), and its name comes from a Native American word meaning "wolf's rump" (a reference to the way this member erodes into gray, rounded hills).
A succession of volcanic-ash-rich mudstone and sandstone with a thickness of 350-foot (110 m) make up the Petrified Forest Member of the Chinle, which was deposited by lakes, highly sinuous rivers and on the surrounding floodplains. This is the same bright, multicolored part of the Chinle that is exposed in Petrified Forest National Park and the Painted Desert. Petrified wood is, of course, also common in this member.
Moenave and Kayenta formations (Lower Jurassic)
Early Jurassic uplift created an unconformity above the Chinle Formation that represents about ten million years of missing sedimentation between it and the next formation, the Moenave. Periodic incursions of shallow seas from the north during the Jurassic flooded parts of Wyoming, Montana, and a northeast–southwest trending trough on the Utah/Idaho border. The Moenave was deposited in a variety of river, lake, and flood-plain environments.
The oldest beds of this formation belong to the Dinosaur Canyon Member, a reddish, slope-forming rock layer with thin beds of siltstone that are interbedded with mudstone and fine sandstone. The Dinosaur Canyon, with a local thickness of 140 to 375 feet (43 to 114 m), was probably laid down in slow-moving streams, ponds and large lakes. Evidence for this is in cross-bedding of the sediments and large numbers of fish fossils.
The upper member of the Moenave is the pale reddish-brown with a thickness of 75 to 150 feet (23 to 46 m) and cliff-forming Springdale Sandstone. It was deposited in swifter, larger, and more voluminous streams than the older Dinosaur Canyon Member. Fossils of large sturgeon-like freshwater fish have been found in the beds of the Springdale Sandstone. The next member in the Moenave Formation is the thin-bedded Whitmore Point, which is made of mudstone and shale. The lower red cliffs visible from the Zion Human History Museum (until 2000 the Zion Canyon Visitor Center) are accessible examples of this formation.
At 200 to 600 feet (61 to 183 m) thick, the Kayenta Formation's sand and silt were laid down in early Jurassic time in slower-moving, intermittent streambeds in a semiarid to tropical environment. Interbedded sandstone, basal conglomerates, siltstones, mudstones, and thin cross-beds are typical channel and floodplain deposits found in the Kayenta. Paleocurrent studies show that the Kayenta rivers flowed in a general westward to southwestward direction.
Fossilized dinosaur footprints from sauropods have been found in this formation near the Left Fork of North Creek. Mountains in Nevada and California continued to rise in the Lower Jurassic as plate motions forced North America northward. Eventually, this created a rain shadow and brought widespread desertification. Today the Kayenta is a red and mauve rocky slope-former that can be seen throughout Zion Canyon.
Navajo Sandstone (Lower to Mid Jurassic)
Approximately 190 to 136 million years ago in the Jurassic the Colorado Plateau area's climate increasingly became arid until 150,000 square miles (388,000 km²) of western North America became a huge desert, not unlike the modern Sahara. For perhaps 10 million years sometime around 175 million years ago sand dunes accumulated, reaching their greatest thickness in the Zion Canyon area; about 2,200 feet (670 m) at the Temple of Sinawava in Zion Canyon.
Most of the sand, made of 98% translucent, rounded-grain quartz, was transported from coastal sand dunes to the west, in what is now central Nevada. Today the Navajo Sandstone is a geographically widespread, pale tan to red cliff and monolith former with very obvious sand dune cross-bedding patterns. Typically the lower part of this remarkably homogeneous formation is reddish from iron oxide that percolated from the overlaying iron-rich Temple Cap formation while the upper part of the formation is a pale tan to nearly white color. The other component of the Navajo's weak cement matrix is calcium carbonate, but the resulting sandstone is friable (crumbles easily) and very porous. Cross-bedding is especially evident in the eastern part of the park where Jurassic wind directions changed often. The crosshatched appearance of Checkerboard Mesa is a good example.
Springs, such as Weeping Rock, form in canyon walls made of the porous Navajo Sandstone when water hits and is channeled by the underlying non-porous Kayenta Formation. The principal aquifer in the region is contained in Navajo Sandstone. Navajo is the most prominent formation exposed in Zion Canyon with the highest exposures being West Temple and Checkerboard Mesa. The monoliths in the sides of Zion Canyon are among the tallest sandstone cliffs in the world.
Temple Cap and Carmel formations (Middle Jurassic)
Utah and western Colorado were deformed as the rate of subduction off the west coast increased in the Middle Jurassic Sevier Orogeny. At the same time, an inland sea began to encroach on the continent from the north. Broad tidal flats and streams carrying iron oxide-rich mud formed on the margins of the shallow sea to the west, creating the Sinawava member of the Temple Cap Formation. Flat-bedded sandstones, siltstones, and limestones filled depressions left in the underlying eroded strata. Streams eroded the poorly cemented Navajo Sandstone, and water caused the sand to slump.
Desert conditions returned briefly, creating the White Throne member, but encroaching seas again beveled the coastline, forming a regional unconformity. Thin beds of clay and silt mark the end of this formation. The most prominent outcrops of this formation make up the capstone of West Temple in Zion Canyon. Rain dissolves some of the iron oxide and thus streaks Zion's cliffs red (the red streak seen on the Altar of Sacrifice is a famous example). Temple Cap iron oxide is also the source of the red-orange color of much the lower half of the Navajo Formation.
A warm, shallow inland sea started to advance into the region (transgress) 150 million years ago, finishing the job of flattening the sand dunes. Limy ooze with some sand and fossils were laid down as 1-to-4-foot (0.30 to 1.22 m) thick sedimentation beds from Mid to Late Triassic time. Some calcareous silt percolated down into the buried sand dunes (carrying red oxides with it) and eventually cemented them into the sandstone of the Navajo Formation. The limy ooze above would later lithify into the hard and compact limestone of the Carmel Formation, 200 to 300 feet (61 to 91 m) thick.
Many unique environments were created by the migrating Sevier thrust system, and the four members of the Carmel Formation in southwest Utah capture these changing environments. Both open marine (crinoids) and restricted marine (pelecypods, gastropods) environments are represented in the Co-op Creek member. Sandstone and gypsum in the Crystal Creek and Paria River members signal a return to desert conditions in a coastal setting.
Outcrops of the Carmel Formation are most notably exposed on Horse Ranch Mountain in the Kolob Canyons and near Mt. Carmel Junction. Other formations totaling 2,800 feet (850 m) thick may have been deposited in the region during Late Jurassic and Early Cretaceous only to be uplifted and entirely removed by erosion.
Dakota Sandstone (Lower Cretaceous)
Mountains continued to rise in the Sevier orogenic belt to the west during the Cretaceous while the roughly north-south trending Western Interior Basin expanded. Rifting in the Gulf of Mexico helped the southern end of the basin to subside, which allowed marine water to advance northward. At the same time, the shoreline advanced inland from the Arctic region. The seas advanced and retreated many times during the Cretaceous until one of the most extensive interior seaways ever, called the Western Interior Seaway, drowned much of western North America from the Gulf of Mexico to the Arctic Ocean. The western shoreline of the seaway was in the vicinity of Cedar City, Utah while the eastern margin was part of the low-lying, stable platform ramp in Nebraska and Kansas.
The pebble to cobble conglomerate and tan fossil-rich sandstone of the resulting 100-foot (30 m) thick Dakota Sandstone include alluvial fan and alluvial plain sediments that grade laterally into coastal plain, marginal marine, and marine deposits. A small remnant of the Dakota is exposed on top of the 8,766-foot (2,672 m) -high Horse Ranch Mountain (photo). This formation is the youngest one exposed in the Zion area but the oldest exposed in Bryce Canyon to the northeast. Deposition continued but the resulting formations were later uplifted and eroded away. The exposed formations in the Bryce Canyon area likely represent these lost layers.
This cache is located within the boundaries of the Red Cliffs Desert Reserve with the written permission of reserve managers. The Reserve is a 62,000-acre scenic desert area dedicated to the protection of the desert tortoise and other rare or sensitive species of wildlife. Non-motorized recreation is allowed within the lower elevations of the Reserve on designated trails only. If a trail is not marked with official reserve signs, it is not a designated trail. Cache seekers should visit www.redcliffsdesertreserve.com before entering the reserve to be sure that their activity is consistent with rules for responsible recreation that protect this fragile habitat area.
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Special thanks to Red Cliffs Desert Reserve and the BLM for granting permission to place this cache.
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