The Plateau

An OUGS Severnside Field Trip

2015

The 2015

Introduction

This was to be another Severnside trip, but one with a new organiser! Janet Hiscott and Tom Sharpe had devised the idea for this trip when talking about what he would do in his retirement from the Museum of Wales. The large group of 27 members that collected in at the end of September 2015 were the beneficiaries of this chat. We were all eager to explore the Colorado Plateau with Janet and Tom to guide us. The Colorado Plateau is an area between the Rockies and the Basin and Range Province and extends through parts of 4 states, , Colorado, New Mexico and . (Fig. 1) It contains some of the most famous and most visited National Parks of the USA and we were here for 17 days to be introduced to the geology, paleontology and human interaction with and exploitation of the region. The Rockies have been through several cycles of uplift and since the , the most recent period of uplift started 5Ma ago and the area has seen a change in elevation of 5000ft. There was associated volcanic activity, building volcanoes and causing a redistribution of metals by heated fluids. The latter having been exploited by man in the Colorado Mineral Belt. The debris eroded from the Rockies during these successive periods of upift was deposited in the plains surrounding them. These sediments, and marine deposits from a period of inundation by an inland sea, form the level beds that comprise the Colorado plateau. During this deposition the local flora and fauna left its mark with footprints frozen in soft lacustrine sediments, shoals of carcases washed against a riverbank, forests preserved on floodplains or buried to create coal and other plant life contributing to the production of oil and gas. It was during the last period of uplift that the of the region cut down through the layers in some dramatic ways creating the hearts of the parks that we were to visit.

Fig..1 Outline map of field trip route. (Tom Sharpe 2015)

2

The Colorado Plateau 2015

Day 2 Denver to Steamboat Springs

The group had gathered in an airport hotel in Denver on the evening of Monday, 28th September and we set out in bright sunshine first thing on Tuesday morning to cross the Rockies. This day would be unique on our trip, not only for the altitude we would be at but also the type and nature of the rocks we would see.

Our route took us north and then west on the US34, the Trail Ridge Road, following a thousand year old Indian trail. The road rises to 12,183 ft and traverses climate zones from prairie grassland to alpine tundra. It is cooler and windier at the top than in Denver! We had a brief stop at Estes Park (elevation 7522 feet) to shop for supplies before continuing the climb, seeing the hotel that featured in The Shining in the distance.

The of Colorado are part of a huge mountain chain, the Western Cordillera, which extends from Alaska to Patagonia, close and parallel to the Pacific coast. The Colorado Plateau, where we would spend most of the trip, lies between them in the east and the Basin and Ranges in the west. The Rockies form the continental divide of North America. The , formed of Precambrian rocks, rises up west of Denver with steeply dipping Palaeozoic and Mesozoic strata exposed as ‘hogbacks’ or ridges along the eastern flanks. The Front Range rises to peaks of 14,000 feet and is a dramatic boundary.

The Precambrian rocks include gneisses of about 1750 Ma that are intruded by large granite masses of about 1450 Ma. By the end of the Precambrian, the overlying rocks had eroded down to the top of these granite batholiths. The area experienced uplift in the to form the Ancestral Rockies which were themselves subsequently extensively eroded. The Laramide Orogeny, in the , faulted and uplifted the area and erosion then reduced the mountains to 3,000 feet above the plains. Continuing uplift in the last 5 Ma has raised the mountains about 5,000 feet to their present altitudes - a complicated story!

We spent the day in the Rocky Mountain National Park working our way up to the Visitors Centre which lies at 11,796 feet, the highest Visitors Centre in the National Park Organisation. En route we stopped at Many Parks Curve (elevation 9,620 ft) where there were views of the surrounding mountain peaks. Through binoculars it was possible to make out the schistic nature of many of the peaks but there were also granite domes visibly cut by pegmatites. In the below lateral moraines could be identified (Fig. 2.1) together with an alluvial fan formed when a dam burst in the valley above.

Fig. 2.1 View from Many Parks Curve of McGregor Mountain and the valley of the Fall between two lateral moraines.

Driving on, we stopped at the Forest Overlook (elevation 11,716 feet) to follow 2 short trails. Visitors are instructed not to leave the marked trails here in order to protect the sparse vegetation which is low lying and fragile (Fig. 2.2). Whilst hardy enough to withstand the intense cold they also have to contend with as little as 2 inches of moisture a year in this alpine desert. The tundra plants are Fig. 2.2 The alpine environment needs low lying, hugging the ground and their roots penetrate 4-5 protection from the numerous feet of visitors to feet into the rocky ground. Forest Canyon Overlook. An early autumn shower had blanketed the tundra.

3

The Colorado Plateau 2015

Evidence of glaciation was clearly visible in the surrounding peaks, with ice shattered, brecciated debris filling the ice carved hollows in the mountains. The weather changed in the afternoon and we watched thunder and lightening storms pass over, with dramatic changes in light (Fig. 2.3). Some of the accessible tors allowed us to examine the interaction between the granite and the schist it had intruded, now deeply eroded into mushroom shapes because the granite has eroded more rapidly (Fig. 2.4).

Fig. 2.3 A dramatic view of The Rockies in rapidly Fig. 2.4 Differential erosion of granite surmounted changing weather. by schist has produced these mushroom shaped formations.

We enjoyed a brief stop at the visitors centre. This building is shut for 7 months of the year and is surrounded by snow poles that extend high above the roof level. It is dependant on its own generator for power. After leaving the visitors centre, we continued to drive through the park seeing the Lava cliffs and the . Unfortunately, during the descent one of our group became ill and needed to be whisked away by ambulance to hospital to be assessed. Fortunately, with no other obvious cause for his illness, the medics diagnosed altitude sickness and he was able to rejoin us the following morning. We reached Steamboat Springs slightly later than anticipated.

Report by Janet Hiscott Photos by Averil Leaver

4

The Colorado Plateau 2015

Day 3 Steamboat Springs to Vernal, Utah

Steamboat Springs Once 25 of us had decided upon our enormous American lunch sandwiches from a frightening selection of combinations, courtesy of the Deli in Steamboat Springs, we visited Black Sulphur Spring, one of the geothermal springs on the banks of the River Yampa, after which the settlement was named. Apparently, the noise of the hot springs bubbling originally sounded like a steamboat, but quietened once a railroad cut was made nearby in 1908. The hot waters emerge at temperatures of 80-100°F and deposits of travertine, CaCO3, were seen coating the rocks where the spring waters emerged. The heated waters emerge via a fault line between Precambrian and sedimentary Mesozoic rocks, some of which were observed dipping at 60° near the springs and the fault line. The sedimentary rocks, of mainly tan coloured and shales, formed part of the Mesaverde sequences, deposited along the coast of the Western Interior Seaway, in the Period.

The sulphurous odour emanating from the springs did not diminish our appetites for giant sandwiches later in the day! (Fig. 3.1) Many of us identified with and applauded Tom’s use of the Fahrenheit scale for high temperatures and the Celsius scale for cooler temperatures. We followed the Yampa River, downstream and westwards, travelling by bus on Cretaceous and overlying Mesaverde sandstones and coals, seeing much evidence of coal powered electricity generation. The tertiary formed ideal circumstances for the accumulation of oil and gas reserves. Evidence of oil and gas extraction and previous uranium (Uranium from interbedded tertiary volcanic ash sequences) were seen from the coach. Onwards and westwards on the bus, on very bumpy road surfaces, which Tom explained as relating to the underlying Mancos Shale. This formation contains bentonite clay rich layers, derived from weathered volcanic ashes, which are especially susceptible to expansion and contraction under varying weather conditions. Picnic lunch was taken outside the Colorado Welcome Centre, at the town of Dinosaur, which indicated what was in store for us later. (Fig. 3.2)

Fig. 3.1 Black Sulphur Spring, Steamboat Springs Fig. 3.2 Road sign, Dinosaur, Colorado

Dinosaur National Monument to Cretaceous strata are upturned against the Uinta uplift at the northern edge of the Colorado Plateau, exposing a remarkable fossiliferous bed or lagerstätten of the uppermost sediments, the . The global fossil record of terrestrial vertebrates is notoriously scarce and a perfect storm (literally!) of events is needed to preserve these ancient ecosystems. The Morrison formation appears like a ‘toned down rainbow’ series of multi-coloured sandstones, siltstones and mudstones, representing a 7million year record of palaeo-environment of an expansive depositional basin with meandering rivers, floodplains, wetlands and fresh and saltwater . The sediment was sourced from the eroding mountain chain of Western USA, which was undergoing tectonic uplift. Fine volcanic ash was spread across the river plains from volcanoes erupting in western Utah, providing a valuable ability to date the sediments at 149 Ma.

Drought conditions are thought to have compromised herds of grazing and carnivorous dinosaurs living on the floodplains. Subsequent flash-flooding events after seasonal rainstorms disrupted their bodies, which were washed downstream to a sandbank on the bend of a river. This poorly sorted horizon of the Morrison Formation forms the Carnegie Quarry, which was first discovered in 1908 by Earl Douglass of the Carnegie Museum, Pittsburgh, when he spied 8 tail vertebrae of an Apatosaurus, and exclaimed that “It was a beautiful sight!” His excavations for the Carnegie Museum continued from 1909 to 1922 and he removed over 20 skeletons and articulated fragments of 300 other animals, giving a

5

The Colorado Plateau 2015 detailed insight into the terrestrial ecosystem of some of the largest land animals, and also early land mammals and frogs. Many specimens found here are ‘type specimens’ for their species. Finds were mainly of herbivorous sauropods, such as Diplodocus, Barosaurus, and Stegosaurus, whose large fossilised plates were clearly seen on the quarry face. Also discovered were carnivorous theropods Allosaurus, Ceretosaurus and Torvosaurus.

Although Earl Douglass collected many specimens for traditional museum display, he had the vision to preserve part of the original sandstone quarry face with its fossil fragments in situ for public appreciation. The site was made a National Monument in 1915 and the ‘wall of bones’ roofed in 1958, but had to be stabilised recently in view of the shrink-swell disruption to its clay containing foundations. Viewing the steeply dipping quarry exhibit wall it looked like a ‘dinosaur soup’ of articulated and other fragments of many dinosaurs, and gives an excellent vision of the dinosaur graveyard (Figs 3.3 and 3.4). Particularly impressive was the Camarasaurus skull peering down at another bunch of visiting geologists! Dinosaur skulls are rarely preserved being thin walled and fragile. Many have been found at this site and with in situ teeth also give valuable dietary clues. We puzzled as to why the ‘wall of bones’ appeared so ‘pristine’ with few fossils other than dinosaur bones, when one compares it with recent debris which usually includes many tree and plant fragments too?

Fig. 3.3 Quarry Exhibit Wall, Dinosaur, National Fig. 3.4 The Wall of Bones, Quarry Exhibit Wall, Monument, Utah Dinosaur National Monument, Utah

Walking the Fossil Discovery Trail, we looked at the variety of members of the Morrison Formation and saw some in-situ dinosaur vertebrae fossils. As always, the American National Monuments and Parks were excellently presented, accessible and had plenty of information for the specialist and non-specialist visitor alike. Our short visit has only tempted me to further explore the national parks of the USA as there were so many more trails to explore.

The Carnegie Quarry site has recently been digitised and is available at http://carnegiequarry.com/ Once again, many thanks to Janet Hiscott for organising and Tom Sharpe for leading such a memorable exploration of the Colorado Plateau which has served to fuel my desire to return in the future.

Report and Photos by Maggie Deytrikh

6

The Colorado Plateau 2015

Day 4 Vernal to Moab stopping at Canyon Pintado, Douglas Pass and Colorado National Monument

On leaving Vernal, we retraced our route eastwards along US 40 back to Dinosaur, crossing the Green River at Jensen, where gravels eroded from the Uintas Mountains overlie Cretaceous rocks. The road runs along a valley formed by a thrust fault which repeated the succession seen in Dinosaur National Monument. To the north we could see the steeply dipping, folded rocks of the Uintas Mountains, firstly an anticline of Dakota sandstone overlying , then the road cut through a hogback formed of Mesa Verde Group sandstone dipping steeply to the west. At Dinosaur we turned south on CO 64 to Rangely, crossing the Rangley anticline which forms the trap for the Rangley oilfield. The reservoir is 6,000 feet below the surface in Permian Weber sandstones. This is the sixth largest oilfield in the USA with estimated reserves of over 1 billion barrels and over 400 wells. We certainly saw lots of well heads and nodding donkeys.

After Rangley we took CO 139 along the Douglas Creek. Our first stop was the Canyon Pintado (Painted Canyon) to view the petroglyph of Kokopelli, a fertility deity usually depicted as a humpbacked flute player (Fig 4.1). The outcrop of Mesa Verde sandstone is in a fragile state and has been supported from spalling by a crude wire rope sling. Excavations indicate that the area has been occupied from around 600-1300 AD.

Fig. 4.1 Petroglyph of Kopopelli at Canyon Pintado

Continuing up the Douglas Creek, the road passes from Cretaceous Mesa Verde Group to Tertiary and finally at the top of the pass. The Mesa Verde group Fig. 4.2 Mesa Verde Group on CO 139 comprises massive, buff coloured, cross bedded sandstones south of Douglas Pass. interbedded with thin bands of shale and coal seams and thinner bedded reddish sandstones deposited in a near coastal environment (Fig 4.2). The Wasatch and Green River Formations comprise finely bedded sandstone and shales deposited in a fluvial-deltaic to lacustrine environment. The shales are organic-rich and even the roadside fragments have a distinct odour of oil (Fig 4.3). These formations are unstable leading to landslips which periodically close the road (Fig 4.4).

Continuing south on CO 139 we had views of to the east, 10,000 feet high capped by Late basalts. At Loma, we turned east along the Grand Valley formed by the , here about 250 miles from its source, and made our way to the Colorado National Monument.

Colorado National Monument lies at the north western end of the Uncompahgre Plateau which rises 2,000 feet above the Grand Valley. The north eastern edge is marked by a large reverse fault, the Redlands Fault, which is expressed by the Ladder Creek Monocline in the south east. This has brought the Morrison Formation that is exposed at the top of the plateau down to the level of the east entrance station. The road crossed the formations (Fig 4.5) in reverse order as it traversed the limb of the monocline then in correct order as it climbed to the top of the plateau. Fig. 4.3 Wasatch and Green River formations on CO 139 just south of Douglas Pass. 7

The Colorado Plateau 2015

Fig. 4.4 Landslips below CO 139 (shelf in top left) south of Douglas Pass.

The Colorado River and its have incised the edge into spectacular vertical-walled hanging . The Rim Rock Drive is 23 miles long Fig. 4.5 View of Ute Canyon showing the following the edge of the canyons. Construction started in 1931, at the height main lithologies of Colorado National of the depression, and was finished in 1951 with a break in work during World Monument. The insert showing the War II. There are numerous view points of which we stopped at Ute Canyon Morrison Formation is from a road cut View, Artists View and Independence Monument View, as well as the Visitor near Artists Point. Centre at the West Entrance (Fig 4.6).

The dark grey rocks exposed at the bottom of the canyon and in the sides of the dry wash (Fig 4.5) are Early gneisses and schists (1.8 to 1.72 Ga) which were intruded with pink pegmatite and granite veins (1.3 Ga). These were originally sediments and igneous rocks from an island arc that collided with Wyoming Province, forming a mountain chain which was eroded back to the basement by the beginning of the period. These Precambrian rocks are separated from younger Mesozoic rocks by the Great . The actual contact cannot be seen as it is obscured by the scree slope. Palaeozoic deposits are completely missing and may have been 2,000 feet thick but were again eroded back to basement during the (Late Carboniferous) when formation of the Ancestral Rockies caused uplift in the Uncompahgre area.

The oldest rocks above the unconformity are of Triassic age. Red sands and muds of the (210 Ma) were deposited in a river delta or flood plain in a wet tropical environment when the area lay close to the equator. These are the bright red layer that can be seen intermittently above the scree slope at the base of the cliffs. The climate became more arid as the area moved north of the equator and aeolian sand dunes of the (200 Ma) covered the area. These are the massive sandstones with large scale cross-bedding that form the main part of the canyon walls. Wetter conditions returned at the end of the Triassic into the Jurassic with deposition of the (190 Ma). These fluvial sands and muds formed in a braided river system and are more resistant to weathering forming a bench at the top of the cliffs along which the Rim Rock Drive runs. Fig. 4.6 Map of Colorado National Monument with inserts of views from stopping points. From south to north these are Ute Canyon, Coke Ovens from Artists View and Independence Monument. 8

The Colorado Plateau 2015

South westwards of the road, cliffs of (165 Ma) are exposed. These were deposited as coastal sand dunes along the shores of an inland sea located in central Utah. They lie unconformably above the Kayenta Formation as renewed uplift of Uncompahgre caused erosion of intervening and which are preserved in (see Day 5).

Around Artists Point, Late Jurassic Wanaka (160 Ma) and Morrison (150 Ma) Formations can be seen. These were deposited in a temperate climate in shallow lakes, and river floodplains as red and green thinly bedded sandstones and mudstones. Fluvial conditions continued into the Cretaceous with deposition of the Burro-Canyon Formation (140 Ma). These are the youngest rocks present in the Monument but are only found in the Black Ridge to the west of the area. This was followed by deposition of the Dakota Sandstone which was deposited along the western shore of a sea that transgressed from east to west across the area. Younger rocks have been removed by erosion during uplift in Miocene and times. Cretaceous rocks are preserved in the to the north of Grand Valley, while fluvial and lacustrine Tertiary rocks preserved in the . These can be seen in the distance in Fig 4.7.

Fig. 4.7 Panorama taken from Artists Point. The Book Cliffs form the long hillside in the background with the Roan Cliffs just visible in the far distance.

On leaving the Monument the road crosses the Redland Fault several times with repeated sections. We joined the I70 at Fruita and travelled westwards on Cretaceous rocks, including the Mancos Shale which was identified by the uneven road surface caused by hygroscopic bentonite clays from volcanic ash. The route follows the Colorado River, turning south on the UT 128 at Cisco and crossing several northwest - southeast anticlines taking the rock succession down from Cretaceous through Jurassic and Triassic to Permian and then back onto Jurassic Navajo sandstone at Moab. During the World War II, and afterwards, uranium was extracted from the volcanic ash in the Chinle Shale around Moab. Spoil heaps were visible on the outskirts of the town though reclamation work to remove the radioactive debris is at last taking place.

Report and Photos by Colin & Kathryn Price

9

The Colorado Plateau 2015

Day 5 Arches National Park

Today we were to visit Tom’s favourite Park, Arches National Park, 76,359 acres of spectacular sandstone scenery in Utah. At the Visitor Centre close to the Park entrance there were excellent displays including rock specimens, videos, photographs and explanatory diagrams. There are in excess of 2,000 catalogued natural arches ranging in size from just under one metre to nearly 100 metres in span. (Fig. 5.1) The minimum size of a recognised arch is 3 feet, imperial measurements being the norm in the United States. The arches of the Park are mainly found within outcrops of the Entrada Sandstone Formation, a Jurassic desert sandstone composed of fine-grained particles with good porosity. These massive, predominantly dune, sediments overlie the clay-rich, thinly-bedded Dewey Bridge Member of the Carmel Formation.

The arches came about as a result of Upper Carboniferous (Pennsylvanian) evaporites having greater buoyancy than the overlying strata and consequently they formed a salt diaper (Fig. 5.2 A-B) through plastic deformation. The younger strata domed upwards, creating sub-vertical joints while percolating groundwater dissolved part of the salt body, leading to collapse of the overlying beds, often along normal faults e.g. Moab Fault. In Fig. 5.2 C the Entrada Sandstone has Fig. 5.1 Landscape Arch: formed out of the Slick Member of the collapsed into the corresponding graben Entrada Sandstone Formation. Nearly 90 metres in length and about 2 structure along the hinge line of the fold, metres thick at its thinnest section. thereby widening the joints and making them accessible to the agents of erosion. This process created a landscape of parallel vertical sandstone slabs known as ‘fins’ (Fig. 5.3).

Fig. 5.2 Schematic diagrams (not to scale) showing the formation of joint fins in Entrada Sandstone Formation

Arch formation has then developed within the Entrada Sandstone Fig. 5.3 Closely spaced parallel fractures in the through further weathering and erosion of the sandstone fins Entrada Sandstone are the result of salt tectonics. (Fig. 5.4) Cut-throughs at ground level developed where rain water Weathering and erosion has widened the joints to pooled and chemical and physical processes enlarged the gap form vertical sandstone slabs. over time. Collapse of each arch eventually resulted, a process that must have taken many millennia from first creation of the arch. Numerous rock falls have been recorded, many widening the gaps of arches, whilst others brought down the arch itself. An undemanding walk of about one kilometre down the Park Avenue Trail (Fig. 5.5) enabled us to see many of the landscape features of the Park. The enclosing walls of the trail showed the Slick Rock Member of the Entrada Sandstone to be a massive, well-cemented, red to orange coloured banded sandstone. Some sections showed planar bedding, but much was cross- stratified with large dune cross-sets typical of an Fig. 5.4 Schematic diagrams (not to scale) showing the aeolian origin. formation of natural arches in the Entrada Sandstone Formation

10

The Colorado Plateau 2015

Fig. 5.5 The View along the Park Avenue Trail. Fig. 5.6 Double Arch, a structure that has more unusually formed On the left is the massive sandstone wall of from water descending from above the arches than from the side Courthouse Towers and in shadow (centre middle) and consequently is described as an example of a ‘pothole arch’. is The Organ. This part of the Park was used as the backdrop in the film Indiana Jones and the Last Crusade. Flash are a common occurrence in Arches National Park as a result of summer thunderstorms. During these events, large volumes of water, sediment and debris are washed through the channels and canyons. The Park area eventually drains into the Colorado River to the south. Storms are short-lived though and beds ephemeral, but nevertheless much of the landscape of the Park has been fashioned by water. Two further short walks later in the day in the Windows Section of the Park took in excellent views of Double Arch (Fig. 5.6) and the Windows themselves (Fig. 5.7). Some of the group braved a scramble and a climb up the back wall of the interior arch to gain further breathtaking views over the Park land. Our final walk of the day was to see Delicate Arch, the iconic image of the Arches National Park. Two choices were available: a route march of about 4-5 kilometres to get up close and personal to the arch or a gentle amble of about 1 kilometre to gain a good, but distant, view point (Fig. 5.8). On our way out of the National Park we had a roadside stop to view Balanced Rock (Fig. 5.9). Unfortunately the sun was setting and the Fig. 5.7 The North Window and South Window at the Windows available light did not bring out the colours of the Section of the Park, better known as The Spectacles. strata we had seen earlier in the day. Web sources state the size of the balancing rock (of Entrada Sandstone Formation) is the equivalent size of three school buses with a height of nearly 17 metres and weighs in at 3577 tons. The pedestal on which the rock rests is of Dewey Bridge Member of the Carmel Formation.

Fig. 5.8 Delicate Arch. The Slick Rock Member of the Entrada Sandstone Formation forms the base and pedestals of the freestanding arch while the Moab member of the forms the bridge. The arch has a horizontal span of about 10 m (32 ft) and a vertical span of 14 m (46 ft). Note the people for scale.

Report and Photos by Geoff Downer and Carole Jeff Fig. 9 Balanced Rock.

11

The Colorado Plateau 2015

Day 6 Canyonlands National Park

Our day excursion from Moab had three objectives but as we were returning to the same hotel Tom decided to vary the schedule. We went first to a location where we were due to observe some Dinosaur tracks which would be clearest in early low angle light. North of Moab our intrepid driver, Ken, headed off road on a dirt track used by more appropriate vehicles to access the campsites and car parks provided for exploration of the area. The car park provided had information and directions for the public to find the Dinosaur trackways site. A short walk brought us to a gently sloping bedding plane of the Morrison Formation sandstone which showed a rippled surface indicative of stream deposition. As we studied the surface we gradually picked out the indentations left as some ancient creatures had walked along a watercourse. This site had been discovered in 1989 by the wife of Martin Lockley, a leading Dinosaur track expert based in Denver, who had then studied and interpreted the site. We all found good vantage points around the slab as Tom pointed out the patterns in the rock. Some of the individual prints showed as a depression with 3 clear claw marks (Fig. 6.1). Several trackways have been mapped (Fig. 6.2) and their formation ascribed to a large Sauropod and smaller carnivorous Theropods. One track left by a bipedal Theropod showed an uneven stride pattern which has been interpreted as the result of a limping animal, perhaps it was the recipient of a swipe from the tail of its intended prey ? The larger animal had left a track which suddenly changed direction but we will never know if these two events were linked in time!

Fig. 6.1 Theropod footprint showing 3 claw marks. Fig. 6.2 Dinosaur trackway probably made by a Boots 12cm wide for scale. Photo: Malcolm Shaw Sauropod. Photo: Malcolm Shaw

Our next site was in Dead Horse Point State Park. As we took a short walk along the peninsular-type mesa Tom regaled us with the legend behind the name. This mesa has a narrow neck and it is proposed that it was used as a corral for horses, but the lack of surface water is a problem and the legend relates the loss of a herd by thirst whilst within sight of the Colorado below. At the overlook we could see the gooseneck of the Colorado River. During the Miocene the Colorado meandered over a level plain but subsequent uplift caused the Colorado to cut down through the layers beneath to create the canyon we now see. In the further distance Tom pointed out the sunshine glinting off a vast array of evaporation ponds (Fig. 6.3). These were using solar energy Fig. 6.3 View from Dead Horse Point looking to evaporate water from a solution to produce Potash. The towards the evaporation ponds of the Kane Creek Paradox formation has created an anticline which has Potash Mine. Photo: Barbara Wood trapped evaporite salts near the surface and this is being exploited by the Kane Creek Potash Mine. River water is used to dissolve the salts since a mining accident killed several miners.

12

The Colorado Plateau 2015

We entered the Canyonlands National Park and continued to Shafer Canyon Overlook (Fig. 6.4). The cliffs to the left surround Dead Horse Point and drop down to the Colorado River, here hid- den from view. In the far distance can be seen the laccolith of the La Sal Mountains. The knob at the end of the near promontory is composed of sand dune deposits of the Navaho Sandstone with red Kayenta Sandstone beneath.

The Park includes a feature, Upheaval Dome (Fig. 6.5), thought to be an eroded impact crater. The crater is 3 miles in diameter set in a rim of Navaho Sandstone with the centre containing upward doming Chinle Formation. The impact has been dated to 65Ma ago and was then buried by later sediments. Looking down into the Fig. 6.4 View out over Colorado River from Shafer crater we could see the river that has been an agent of erosion Point. Photo: Norman Nimmo-Smith draining out to the west.

As we walked to the bus our driver, Ken, drew Tom’s attention to a large red rock which was being used as a edge to the path. Its surface was a bedding plane and was covered in mud crack, holes and channels (Fig. 6.6). We all gathered round as Tom tried to explain to our new geology student what the rock represented. He identified the block as a piece of Kayenta Sandstone which had been deposited in a river floodplain and then subjected to desiccation. Animals and plants had left their marks as burrows and holes. The mud cracks had then been infilled with the next inundation. A suitable end to our day.

Fig. 6.5 Upheaval Dome in Canyonlands National Park. Photo: Norman Nimmo-Smith

Fig. 6.6 Kayenta Sandstone block with bedding surface showing mud cracks and trace fossils. Photo: Averil Leaver

Report by Averil Leaver

13

The Colorado Plateau 2015

Day 7 Moab to Mesa Verde

Our first stop was the Moab Rock Shop selling everything from dinosaur heads to what looked like hard core. An exhibit of the mineral fuchite caused school boy giggles whichever way it was pronounced.

We then headed south to Newspaper Rock, a face of dune bedded Wingate Sandstone. The bedding has allowed the front to weather off leaving an overhang which protects a face of about 15m by 15m. Over the years chemical and biochemical processes have developed a dark red to black coating known as desert varnish. The native Indians scratched or pecked through to clean sandstone to leave hundreds of shapes and figures known as petroglyphs. (Fig. 7.1). I have seen the same technique in Jordan. Dating is problematic, re-establishment of the desert varnish can give relative dates, archaeology adds little but they were hundreds of years old when the Spanish arrived.

From there we headed South East into a distinctive change in scenery. On top of the Mancos shale and Dakota Sandstone bedrock there was a layer of red soil. This was loess, windblown dust from the west. Several metres thick in places, it is very fertile. So in contrast with the arid conditions of the last few days we could see grass, trees and agriculture.

In the afternoon we arrived at Mesa Verde National Park, technically not a Mesa but a Cuesta. This caused a problem for those of us with only a little Spanish who knew “Quanto Cuesta?” meaning “How Much?” but not that it also meant “slope”. The southward dip is significant though. We drove up the sequence starting with Mancos Shale then on to Point Lookout, the high point at 8,417 ft at the top of the scarp, a layer of sandstone . From there the drive southward was down dip. High up the valleys were V shaped in contrast to the steep sided canyons we were becoming used to and there were thousands of dead trees caused by forest fires. As we drove on younger rocks were exposed. First was the , a coastal plain deposit, and then the , a shallow marine deposit.

In the Cliff House Sandstone the valleys have developed into steep sided canyons. The dark bands were shale, indicating deeper water. It was difficult to get close, but at one location, near Spruce Tree House, low angle laminar bedding was immediately below the shale indicating more turbulent conditions. Fig. 7.1 Newspaper Rock showing At Spruce Tree House (Fig 7.2) rock dwellings have been built into alcoves high in petroglyphs and protective overhang the cliffs between 2 shale layers. Here bedding was difficult to see except where the rock had been blackened by cooking fires.

My interpretation is that the low angle bedding was foreshore followed by a sea level rise with a depositional hiatus until shale was deposited in deep water. As sea level fell sand was again deposited with hummocks and swales indicating this was above the storm wave base. Observations further up were problematic until the prominent shale layer which indicated another sea level rise.

In conclusion, whatever the archaeologists may say, human occupation of Spruce Tree House lasted one para sequence.

Fig. 7.2 Spruce Tree House

Report and Photos by Bill Richardson

14

The Colorado Plateau 2015

Day 8 Mesa Verde to Chinle

Leaving Colorado we travelled westward to Utah and the southern third of the Monument Upwarp which extends from the confluence of the Green and Colorado Rivers in Utah to Monument Valley in Arizona. The Monument Upwarp formed on the southwestern edge of the Paradox basin during the Early Permian and contributed sediments to the Paradox basin possibly up to the . It’s not unusual to come across igneous features in this general sedimentary landscape. However Ship Rock (420 metres) in New Mexico seen at a distance of 40 km was remarkable (Fig. 8.1). Formed 25 Ma ago in the Navaho Volcanic Field it is an example of a diatreme, a volcanic pipe produced by gaseous explosion and composed of fractured volcanic breccia. To either side are black dykes of minette which is chiefly composed of biotite and orthoclase. Fig. 8.1 Ship Rock The 300 metre high Alhambra Rock (Fig. 8.2) is another diatreme and part of a 1.6 km long dike (0.5 to 6 metres wide). The main mass is a breccia of granite, sandstone and overlain by a minette of biotite and augite. The road approach to the Park and its overlook parking area lie on the Permian Halgaito Formation. This overlies the main Goosenecks sequence of the two uppermost Pennsylvanian Hermosa Group formations. One is the Honaker Trail Formation (291 Ma to 295 Ma) deposited within a shallow sea environment to give fossiliferous dark grey alternating with siltstones and shales. The other is the Paradox Formation (297 Ma to 300 Ma) from an enclosed evaporite forming shallow marine basin to give gypsum together with black shales (Fig. 8.3).

Fig. 8.2 Alhambra Rock Fig. 8.3

The overlook is on the north rim of the Park and some 310 metres below is the San Juan River; a of the Colorado River. Before us was the most famous example of an meander. The total length of the meander is greater than 10 kilometres compressed into about 2.5 kilometres between its straight line farthest points. The lie to the east of the Colorado Plateau providing runoff towards what is now Monument Valley. Early in its life the precursor of today’s San Juan River formed an extensive which initially received sediment from the San Juan Mountains. During the Monument uplift of the Colorado Plateau the early precursor of the San Juan River cut through what had been the lake bed to form in the Halgaito Shales plain. As a result of the downstream Colorado River cutting deeper over time the San Juan River itself incised ever deeper into the Monument Uplift. The lower third of the highest canyon walls above the river are Paradox Formation limestones from a Pennsylvanian Period sea between 310 Ma and 300 Ma. Along with limestone and dolomite some evaporites such as salt and gypsum were formed. The remaining upper layers are of the Honaker Trail Formation from the Upper Pennsylvanian Period between 300 Ma to 270 Ma. Looking across the river sharply defined horizontal limestone layers stand out. These layers are resistant to weathering and have been undercut due to the erosion of the intervening softer shale layers. The layers are the result of twenty nine fluctuations of glacial sea level changes during the Pennsylvanian Period. The sequence of alternate layers of limestone and shale is capped by a layer of sandstone. Blocks seen at the base of the canyon and in the river are from the undercut limestone. Various outcrops and patches of limestone line the north rim. Barely visible above the farther canyon rim were glimpses of Monument Valley buttes and Alhambra rock. The San Juan River cuts through the Raplee Anticline (Fig. 8.4) a few miles upstream from the town of Mexican Hat. The Anticline is an example of a monocline of which there are many in the Colorado Plateau. The Raplee Anticline rocks are of the Pennsylvanian Hermosa Group about 300 Ma.

15

The Colorado Plateau 2015

There is no exposed fault however the flat iron formation exposed by stream erosion by the San Juan River is considered to be the result of a compressional east dipping high angle reverse fault probably during the Laramide Orogeny, 70 Ma to 50 Ma. Oxidation of iron in some of the sedimentary layers gives them a reddish colour.

Fig. 8.4 Raplee anticline

We stopped at Mexican Hat Rock (Fig. 8.5), an unusually shaped rock from which the nearby town of Mexican Hat gets its name. This is a remnant of a sandstone layer of the Permian Halgaito Formation formed from sediments deposited in a shallow seaway and later becoming a coastal plain. The ridge line in the distance is part of the Fig.8.5 Medicine Hat Rock crest of the Raplee Anticline. By the time we reached the Monument Valley National Park Overlook area rain had caught up with us. No Western film big blue sky only cloud with the monuments capped with mist. There are some forty monuments in the Park. Their normally bright red iron oxide produced hues and darker manganese oxide hues were much subdued. Leaving the Visitor Centre we boarded our tour car (Fig. 8.6) an open sided utility vehicle with bench seats and an overhead sheet metal covering. Our south bound route was along a now rain soaked Valley Road best described as a dirt car track travelling over the valley Organ Rock Shale base with the slightest single incursion onto Sandstone. We stopped at the viewpoint for the Mittens (Figs 8.7 and 8.8) and Merrick Butte (Fig. 8.9) but their tops were disappearing into the mist. They are looked on as isolated “monuments” at more than 300 metres high and are the remnants of a continuous Permian sedimentary cover. The most resistant strata is the Chinle Formation Shinarump Conglomerate, a light grey conglomeratic sandstone which is still to be found as a thin capping on Merrick Butte. Below this layer is the easily eroded ; a red brown shale and siltstone. It provides much of the talus around the base of the buttes. Beneath the Moenkopi Formation layer is the highly resistant De Chelly Sandstone. This layer forms the recognisable near vertical butte type sides. Mostly covered by dark desert varnish it is light brown where slabs have fallen away. Beneath the base talus lies the easily eroded Cutler Formation Organ Rock Shale. Fig. 8.6 Tourist car

Fig. 8.8 East Mitten Butte

Fig. 8.7 West Mitten Butte

Fig. 8.9 Merrick Butte 16

The Colorado Plateau 2015

We passed Elephant Butte (Fig. 8.10) and Camel Butte (Fig. 8.11) before coming to Three Sisters Junction at which point we turned east toward John Ford’s Point and a view of the Three Sisters pinnacles (Fig. 8.12) Faith (183 metres), Hope (100 metres) and Charity (175 metres) at the southern end of Mitchell Mesa.The formation is also said to represent a Catholic nun facing her two pupils.

Fig. 8.10 Elephant Butte

Fig. 8.11 Camel Butte

Fig. 8.12 The Three Sisters Fig. 8.13 North window

The Rain curtailed our visit but we did get a view through the North Window (Fig. 8.13). On our way out toward the southern boundary of Monument Valley we passed Agathla Peak (Fig. 8.14). It is another Navaho Volcanic Field diatreme associated with minette dikes, surrounded by deposits of the Chinle Formation lenticular sandstone and conglomerate of 230 Ma to 210 Ma. The southerly remnant of the Comb Ridge monocline (Fig. 8.15) was the last major structure to be seen running parallel to the road. Overall the main structure runs almost 112 km from Blanding in south eastern Utah down almost as far south as Kayenta in Arizona. It represents a major fault along the eastern edge of the Monument Upwarp. The east dipping angular formations show large cross bedding and here are chiefly Jurassic Navaho Sandstone. They Fig. 8.14 Agathla Peak often revert to the horizontal

Fig. 8.15 Comb Ridge We continued to end our now darkening day in Chinle.

Report and photos by Malcolm Shaw

17

The Coloradoolorado Plateau 2015 2015

Day 9 Canyon De Chelly National Monument.

This is situated within the Navajo Nation and is a network of canyons whose walls range from 30 to 1,000 feet high. The walls consist of Permian De Chelly Sandstone that has large scale cross bedding, indicating that it was formed by wind- blown sand and this is capped with Triassic Shinarump Conglomerate. The Permian sandstone rests directly on Precambrian basement. The area has been uplifted several times, most recently 3 million years ago, at the same time as the rest of the Colorado Plateau and it was then that rivers carved the canyons. People have lived in the canyons for nearly 5,000 years, longer than anywhere else in the Colorado Plateau, and it was for this reason that Canyon De Chelly was established as a National Monument to preserve the record of their settlement. It was from this site in 1864 that the Navajo were starved and forced out on The Long Walk to New Mexico before returning in 1868. We followed the South Rim Drive stopping to look at cliff dwellings (Fig. 9.1), the Precambrian/Permian unconformity, the De Chelly Sandstone cross bedding and the Shinarump Conglomerate on top.

Painted Desert. At the southern edge of the Navajo Nation is an area known as the Painted Desert because of the multi-coloured rock exposures of the Upper Triassic Chinle Formation (Fig. 9.2). In the Late Triassic this area was situated close to the Equator and formed part of a vast alluvial plain with deposits of sandstone, mudstone and conglomerate. In addition the layers contain bentonite clay derived from volcanic ash. Each colour band represents an ancient soil horizon, the differing colouration is due to the presence of various minerals such as iron and manganese and the position of the water table. A low water table allowed the iron minerals to oxidise to produce a reddish colouration whereas a high water table produced a reducing environment and minerals of a green/blue colour. Bentonite clay swells as it absorbs moisture then shrinks and cracks as it dries causing surface movement which inhibits plant growth. In Fig. 9.1 Dwelling on a ledge within the De Chelly addition the surface weathers readily also inhibiting plant growth. Sandstone These factors together with the arid climate result in the bare, badland topography. Overlying the Chinle Formation is the Pliocene Bidahochi Formation made up of coarse sediments and volcanic debris. This has generally been eroded away but where it remains it underlies the roads and view points and supports pinyon-juniper shrubland (Fig. 9.3).

Petrified Forest National Park Within the Painted Desert is the Petrified Forest National Park. Here the Chinle Formation is 1,550 feet thick and is divided into the Upper and Lower Petrified Forest Members separated by the discontinuous Sonsela Sandstone Bed, which was deposited by a braided river system and is the horizon richest in petrified wood. From the fossil remains it seems that a forest of tall trees, together with ferns and cycads, grew on an alluvial plain. Most of the fossil trees are straight trunks which had been stripped of their bark and Fig. 9.2 Painted Desert branches. This suggests that occasional floods must have swept trees on to a flood plain where they were buried in the fine-grained fluvial sediment and preserved in relatively anoxic conditions. Some tree trunks had started to decompose suggesting they had been exposed to air before they were buried and some had been buried in situ. The woody tissue was replaced by silica, from the silica–rich groundwater that circulated through the sediment and volcanic ash, often resulting in preservation of the tissue structure. We walked along the Blue Mesa trail where we saw many fossil trees being eroded out of the Sonsela Sandstone Bed. A developing thunderstorm postponed other activities until the next day.

Report and Photos by Margaret and Norman Ridley Fig. 9.3 Vegetation growing on the basaltic Pliocene Bidahochi Formation with the barren Painted Desert in the background. 18

The Colorado Plateau 2015

Day 10 . Wednesday 7th October . Petrified Forest National Park

Crystal Forest Trail. Spectacular, multi-coloured fossilised tree trunks up to 30 feet long lay along the trails. After silicification the tree trunks crack under stress and as they are eroded out of the sandstone the cracks widen and the segments separate. The tree trunks appear as though they have been cut up by a chain saw (Fig. 10.1). This can be explained by considering that the trunks have been replaced by s i l i c a w h i c h f r a c t u r e s l i k e g l a s s . The petrified wood displayed a range of colours due to minute races of iron (red and brown), uranium (yellow) and copper (blue and green). Where the logs were hollow large crystals of rose quartz and other gemstones have formed or large masses of amor- phous chalcedony, cryptocrystalline silica, have lined the cavity walls (Fig. 10.2).

Fig. 10.1 Fractured fossilised tree trunk.

Giant Logs Trail and Rainbow Forest Museum. Several species of fossil trees have been identified with the com- monest being Araucarioxylon arizonicum (related to our Monkey Puzzle Tree). Some logs displayed trace fossils in the form of finger- width burrows. The Petrified Forest is said to be one of the best places in the world to see the fossil record from the Late Triassic Period. Living on the floodplain and swampy ground were phytosaurs, crocodile –like reptiles, and aetosaurs, early dinosaurs. Part of a Coelophysis , a small therapod dinasour found in the Park, was on display in the Rainbow Forest Museum. Tom pointed out that this specimen was very similar to a specimen found in South Wales last year indicating Fig. 10.2 Mineral deposition in fossilised wood. the cosmopolitan nature of large vertebrate life at this stage in Pangea in the Late Triassic. The Petrified Forest has hosted many great scientific minds. Our two leaders Janet Hiscott and Tom Sharpe are recreating the pose (Fig. 10.3) taken by Dr and Mrs Albert Einstein 84 years earlier standing in front of “Old Faithful”, a giant log, 35 feet long and weighing approximately 44 tons, near the end of the Giant Logs Trail.

.

Report and Photos by Margaret and Norman Ridley Fig. 10.3 Our two leaders, Janet Hiscott and Tom Sharpe, by ‘Old Faithful’.

19

The Colorado Plateau 2015

DAY 10 Continued Meteor Crater

Our journey then took us along the valley of the Little Colorado River on the I-40 (the modern replacement for Route 66) and back in sunny weather after the previous few days of rainstorms. The route was mainly on the Triassic Moenkopi Formation only 40 miles from the southern edge of the Colorado Plateau.

En route to our main locality of the day, Meteor Crater, we stopped off in Winslow, Arizona to see the famous “Standing on the corner” (featured in the Eagles hit “Take it Easy”) right on the old Route 66. Many photographs were taken whilst Eagles songs especially “Hotel California” blasted out from nearby shop doorways. After this unscheduled stop our leader, Tom, rounded us up to continue with the geological business of the day which brought us a few miles south of I-40 to Meteor (or Barringer) Crater. This crater, which is 570 feet deep and has a diameter of 4100 feet, is the best preserved meteorite impact crater on earth (Fig. 10.4). It was formed about 50,000 years ago by the impact of a nickel-iron meteorite about 160 feet in diameter which entered the atmosphere from the north at a speed of about 28600 mph. It was first reported in 1871 and was considered to be volcanic in origin and related to the nearby San Francisco volcanic field near Flagstaff. Daniel M. Barringer, a mining engineer drilling in the early 1920s, found many meteorite fragments. The impact origin of the crater was finally confirmed in 1960 by Eugene M. Shoemaker. Shoemaker went on to develop the astrogeology research programme of the USGS based at Flagstaff, Arizona and in the 1960s lead the geological training programme for NASA’s Apollo astronauts which included field work at Meteor Crater. To commemorate this there is a 6 foot cardboard cutout of an Apollo astronaut in a spacesuit at the bottom of the crater. Shoemaker established that the inverted stratigraphy to be found around the crater is typical of an impact (Fig. 10.5).

Fig.10.4 A distant view of Meteor Crater Fig.10.5 Crater rim showing the inverted stratigraphy

Our visit consisted primarily of a tour along the crater rim accompanied by our amusing guide, Eduardo, who pointed out matters of interest as well as keeping us amused with some of his stories (Fig. 10.6). After the tour we were able to visit the well put together museum on the site dedicated to meteorites and space geology.

After a late lunch we left the crater to continue our journey along I-40 to Flagstaff and from there north toward the . En route to and around Flagstaff we had frequent views of the San Francisco Peaks volcanic field. There are many volcanic ash cones, some less than 1,000 years old, on top of the underlying . Just to the north of Flagstaff is Humphreys Peak, at 12,633 feet, the highest point in Arizona. This is a remnant of a much larger volcano built up 3 million years ago, the top 3,000 feet of which collapsed in an eruption about 500,000 years ago. Our journey north on US-89 brought us to the south rim of the Grand Canyon at Grand Canyon village in time for sunset. At an elevation of 7,000 feet the south rim of the canyon, due to a fold in the strata, is 2,000 lower than the north rim. This iconic and spectacular wonder of the world exposes a magnificent sequence of rocks illustrating a major part of the geological history of the Colorado Plateau from the Archaean Vishnu Schist in the floor of the canyon to the Permian Kaibab limestone of the canyon Fig.10.6 Start of the tour with our guide, rim. The canyon is 277 miles long, up to 18 miles wide and a mile deep.

We visited Mather Point that evening at sunset. It was a spectacular and memorable first view of the canyon as we watched the changing colours of the canyon walls as the sun dipped below the horizon. This was but a foretaste of the canyon, where we were to spend the next one and a half days.

Report by Geoff Solomons Photos by Averil Leaver

20

The Colorado Plateau 2015

Day 11 Grand Canyon National Park

We made an early start followed by a short drive to the Grand Canyon National Park where the group dispersed into various combinations and permutations, trekking into the Canyon and along the South Rim. Most tackled the (Fig. 11.1) to the first stop, a 3 mile round trip, which in the cool of the early morning was not too daunting a descent or ascent and left plenty of time to walk around part of the rim later. A few intrepids spent the day trekking further down into the Canyon as far as Indian Garden, a 9 mile round trip. Some others confined themselves to exploring the rim. A shuttle bus meant that it was possible to walk a reasonable distance along the rim and to catch the bus back.

Through the day various members reported seeing a variety of wildlife: mule deer, elk , squirrels, chipmunks, tarantula, the ever present ravens, turkey vultures, red tailed hawks, American kestrels, condor, a Northern Pygmy Owl (a rare resident) and heard , but not seen, was a common poorwill (similar to a Nightjar). The Geology, of course, was spectacular with the stratigraphy on full display. Much discussion was had as we helped each other to identify the rock layers with the help of the field guide. Mnemonics are useful for remembering the order and here’s one I found on a postcard: Know The Canyon History. Study Rocks Made By Time . Starting from the top, this corresponds to Kabib Formation; ; ; Hermit Shale; ; ; Muar Limestone; Bright Angel Shale; Tapeats Sandstone. Below this is the Great Unconformity; the Grand Canyon Supergroup and finally, the Vishnu Basement rocks. Fig. 11.1 View from top of the Bright Angel Trail The Vishnu granite and schists were particularly clear from the West rim at Hopi point, from where the Colorado River could also be seen in the distance, as well as part of the Granite Rapids. With the help of binoculars we could also see four rafts negotiating the rapids.

Just before Hopi Point on the trail is Powell Point which commemorates the famous one-armed civil war veteran, Major John Wesley Powell, who lead expeditions down the Colorado River in 1869 and again in 1871-2. The enormity of that undertaking was recently highlighted on a TV programme with Dan Snow who was part of a team who attempted the same route using Powell’s diary as a guide. At the end of this fine and sunny day, we re-grouped, having appreciated a change of pace and an opportunity to stretch the legs or rest up as needed, to watch the beautiful sunset from Yavapai (Fig. 11.2) which was still dramatic despite a slight lack of Fig. 11.2 Sunset from Yavapai Point clarity in the air due to the recent California fires.

Report and Photos by Teresa Jenkins

21

The Colorado Plateau 2015

Day 12 Grand Canyon to Page

This was the day of the flight that most of us took over the Grand Canyon, and was one of the highlights of the trip. Our thanks go to Geoff Solomons who organised the flight for our group. It was a perfect day for flying with blue skies and settled conditions. The Grand Canyon National Park Airport was only a short drive from our hotel in Tusayan on the south side of the Canyon, and we were soon checked-in and ready for our 45-minute, 100-mile circuit around the Canyon in a Twin Otter aircraft. Because of the relatively large size of our group, we were spread out among three aircraft in the company of other excited tourists.

After take-off, we flew eastwards over the Kaibab Limestone of the Coconino plateau lying to the south of the Grand Canyon. It was only when the aircraft turned and flew over the south rim of the Canyon towards the north-east that we fully appreciated the full width (averaging 10 miles) and depth (about a mile) of the chasm beneath us. We saw a vast panorama of descending cliffs, platforms, buttes and pinnacles (Fig. 12.1). At the bottom of the Inner Gorge lay the muddy Colorado River, winding its way down the Canyon through frequent rapids. We even spotted a few rafts going down-river. Differential erosion of the horizontal rock layers had produced a series of steps on either side of the Canyon that stretched horizontally as far as the eye could see. The different sedimentary layers produced bands of colour that included white, cream, yellow, orange, red and brown. At the bottom of the Canyon Fig. 12.1 Eastern section of the Grand Canyon we could clearly see the much darker igneous and metamorphic from the air. South rim on the right. Precambrian Vishnu rocks, whilst the creamy-coloured Permian Coconino Sandstone near the rim provided a very visible horizontal marker along both sides of the Canyon. The aircraft then took us westwards along the north rim before heading back across the Canyon and returning to the airport. Our flight over the Canyon was a tremendous experience and we all disembarked from the aircraft grinning like a bunch of Cheshire Cats (Fig. 12.2).

During the flight, the flatness of the plateaus stretching away into the distance from both Canyon rims was very evident. Equally striking was the difference in vegetation between the south rim, which was heavily forested, and the north rim, which was predominantly grass and scrub with only a few trees. A difference in climate results from the higher elevation of the north rim (around 8,000 feet) compared with the south rim (around 7,000 feet), although this difference in height is not really obvious when standing on the south rim looking towards the north rim many miles away. The explanation is that an ancient uplift on the Kaibab Fig. 12.2 Twin Otter aircraft used for our flight over Plateau, well to the north of the present Canyon, has caused this the Grand Canyon part of the plateau area to slope gently southwards, giving the h i g h e r north rim much cooler and wetter conditions.

We drove back to the Canyon’s south rim, turning eastwards along the East Rim Drive to our next viewpoint, Grandview Point. It certainly lived up to its name. At this much wider part of the Canyon we looked across mile after mile of colourful buttes and ravines (Fig. 12.3). In the far distance we could see the distinct horizontal band of Coconino Sandstone close to the top of the north rim. We also had an excellent view of two major exposed within the Grand Canyon – the Great Unconformity between Precambrian and Cambrian sedimentary rocks and lower down the unconformity between metamorphic and igneous rocks of the Early Proterozoic and sedimentary rocks of the Middle Proterozoic. Fig. 12.3 View of Grand Canyon from the south rim Before leaving the Grand Canyon National Park we stopped at two at Grandview Point, looking across at the Canyon’s more viewpoints on the east rim drive, Lipan and Desert View. north rim in the far distance. 22

The Colorado Plateau 2015

Lipan Point provided a good view of the Great Unconformity, clearly showing the Precambrian sedimentary rocks of the Grand Canyon Supergroup dipping at about 10 degrees relative to the horizontal Cambrian rocks of the lying above the unconformity. At Desert View, looking north-eastwards, we had an amazing panoramic view of the Colorado River as it wound its way through the Inner Gorge, which was much wider here than further down-river.

Headed east out of the Grand Canyon National Park, along state route SR-64, we entered the Navajo Nation Indian Reservation once again. Far to the south across the flat plateau, about 60 miles away, we could see the snow-capped summit of Humphrey’s Peak in the San Francisco Volcanic Field, which we had passed through two days previously on our way north to the Grand Canyon. Not far beyond Little Colorado Gorge the highway crossed a dry river bed (known locally as a “wash”) filled with basaltic lava erupted from one of the volcanoes in this Field. Near the town of Cameron, where we turned north onto highway US-89, we passed the low-lying volcanic cinder cone of Shadow Mountain, the northernmost vent of the San Francisco Peak Volcanic Field. Its last eruption was about 300,000 years ago. As we continued to drive north the road wound through red and green layers of badlands topography produced by erosion of the soft shales and bentonitic clays in the now-familiar Chinle Formation. Expansion and contraction of the bentonite in response to changes in moisture content had caused the road surface to undulate in this area and the bus bounced up and down in a most remarkable manner as we drove along. It was reminiscent of a roller-coaster.

Our next stop was at an impressive display of ancient dinosaur tracks, about sixteen miles north of Cameron close to highway US -89. A short distance along a side road we came to the site of the tracks, which were exposed in outcrops of Early Jurassic Kyenta Formation rock. Over quite a large flat area we examined sets of small tracks (named Kayentapus) and large tracks (named Dilophosauripus) made by three-toed theropods (Fig. 12.4). Some Navajo Indians had stalls selling jewellery at the site and one of them helpfully poured water into a few of the the track depressions to make them more visible. These tracks were considerably more extensive and numerous than the equally impressive theropod and sauropod tracks seen on Day 6 at Copper Ridge, about 20 miles north of Moab.

Driving north again on US-89, we found ourselves travelling Fig. 12.4 Dinosaur tracks (Dilophosaurus) in alongside the Echo Cliffs for dozens of miles. These cliffs form Jurassic rock, with 15 cm ruler for scale. the steep front slope of an eastward-dipping monocline. They are capped by massive light-coloured Jurassic Navajo Sandstone, underlain by red sandstones and shales of the Kayenta and Moenave Formations. In some sections we could see the older chocolate-coloured rocks of the Triassic Chinle Formation peeking out at the base of the cliff. Eventually the highway climbed up and took a route through the Echo Cliffs towards Page, our destination for the night.

During the 110-mile journey from the Grand Canyon to Page we had our first opportunity to catch sight of the famous geological feature known as the Grand Staircase rising to the north of the . The Staircase is a series of cliffs or escarpments formed by erosion of the Colorado Plateau’s “geological layercake”. They rise up from the rim of the Grand Canyon in the south to the Paunsaugunt Plateau (and Bryce Canyon) in the north. A shallow northwards dip of the strata has accelerated the rate of erosion and differential erosion has produced wide, gently sloping platforms in the softer strata between the more resistant cliffs of the Staircase. The Staircase has been divided into five steps that are colourfully named Chocolate Cliffs (oldest rock), Vermillion Cliffs, White Cliffs, Grey Cliffs and Pink Cliffs (youngest rock). The different colours demonstrate the different environments in which the sediments were deposited which included deserts, lakes, rivers, beaches and shallow seas. Thus the Grand Staircase encompasses a visible sequence of sedimentary strata covering a time period of over 200 million years, from the Permian Moenkope Formation of the Chocolate Cliffs to the Tertiary Claron Formation of the Pink Cliffs. We would be climbing the Staircase the following day with a change in elevation of around 3,700 feet.

Report and Photos by Norman Nimmo-Smith

23

The Colorado Plateau 2015

Day 13 Page to Tropic stopping at Zion and Bryce Canyon

After our night in Page (altitude 4,300 feet), we headed north-west to our first destination of the day, , 118 miles away. It was yet another perfect day, sunny and warm. We crossed the Colorado River just downstream from the Glen Canyon Dam, which holds back the waters of the Colorado to form , the second largest man-made reservoir in the US. It is named after John Wesley Powell who explored the Green River and Colorado River in 1869, and later became the second director of the US Geological Survey in 1881.

Our route took us in a westerly direction along highway US-89, which continually twisted, ascended and descended through a spectacular and ever-changing landscape of colourful sedimentary rocks. Looking to the north and west our view of the Grand Staircase gradually improved. North of Kanab highway US 89 climbed up through the attractive red sandstone of the Vermillion cliffs, the second step in the Grand Staircase, to a gently sloping area covered with sand dunes. The light- coloured sand was derived from erosion of the Navajo Sandstone of the White Cliffs further to the north, the third step in the Staircase.

About 15 miles beyond Kanab the highway dropped steeply down towards Mount Carmel Junction, crossing the north- south trending Sevier Fault at the bottom of the valley. The Sevier Fault is a westward-dipping high-angle normal fault zone extending for over 200 miles, with a displacement of at least two thousand feet. It separates the Markagunt and Paunsaugunt plateaus, two of the many smaller plateaus that make up the overall Colorado Plateau, and is considered to represent the boundary between the Colorado Plateau to the east and the much-faulted Basin and Range Province to the west. Movement along the fault initially took place during the Miocene, about 15 million years ago, when renewed uplift broke the Colorado Plateau into a series of blocks close to its south-western edge. The Sevier Fault continued to be active during the and we would see evidence of this after our visit to Zion National Park.

Turning west off highway US-89 at Mount Carmel Junction we headed towards Zion National Park along road UT-9, crossing Cretaceous sandstone and shale before descending to the park’s east entrance (altitude 5,700 feet). A short distance inside the park we walked to the famous Checkerboard Mesa, a cliff-face of Navajo Sandstone etched with a criss-cross pattern of natural grooves formed by weathering processes (Fig. 13.1). The sandstone exhibits impressive large-scale cross-bedding in ancient sand dunes and near-horizontal grooves have been carved out by windblown sand along the bedding planes. Weathering of vertical joints in the sandstone by rain and freeze-thaw cycles has resulted in similar perpendicular grooves, thus forming the checkerboard grid pattern. The Early Jurassic Navajo Sandstone was deposited in an aeolian environment composed of large sand dunes, nearly as extensive as the modern Sahara Desert. This sand sea, or erg, was vast and extended over most of Utah as well as parts of adjacent states. Following deposition, the sand grains were cemented by calcite and iron oxide to produce various shades of red, yellow and white rock. Before leaving the iconic Checkerboard Mesa we used it as the backdrop for our “official group photograph” which was taken by Todd, our friendly All-American bus driver (Figure 13.2). After driving further into Zion we stopped for a short walk along the Canyon Overlook Trail. The trail, which was quite narrow in places and had some interesting long drops to the canyon below, took us to a magnificent viewpoint that looked westwards over the deep Pine Creek Canyon and to the tall cliffs of Navajo Sandstone and higher peaks beyond. The peaks had evocative names such The Sentinel, The West Temple and The Alter of Sacrifice. The canyons had been eroded by the power of the and its tributaries in an area that was prone to energetic flash flooding. Although the Navajo Sandstone is relatively hard the less-resistant Kayenta Formation beneath it allows undercutting to take place, thus accelerating widening of the canyons (Figure 13.3)

Fig. 13.1 Checkerboard Mesa, Zion National Park Fig. 13.2 Group photo at Checkerboard Mesa, with our excellent guide Tom Sharpe at the front. We then retraced our steps and headed out of Zion National Park, back to Mount Carmel Junction, where we drove northwards towards Bryce Canyon National Park, 70 miles away and over 2,000 feet higher. We climbed up highway US-89 through Long Valley, along the line of the Sevier Fault Zone. Jurassic strata gave way to younger Cretaceous rocks of the Grey Cliffs, the fourth step in the Grand Staircase.

24

The Colorado Plateau 2015

These rocks have been mined for coal around the town of Glendale. As we continued to climb, we reached the fifth and final step in the Staircase, the pinky-orange Early Tertiary rocks of the Claron Formation. Further along Long Valley we turned eastwards along road UT-12, re-crossing the Sevier Fault before starting to head into Red Canyon. At this point the line of the fault was dramatically displayed in the hillside adjacent to the road where light-coloured Tertiary rock of the Claron Formation had been brought into contact with dark-coloured Quaternary basalt that had dropped downwards (Fig. 13.4).

Fig. 13.4 Normal fault exposed in hillside near Fig. 13.3 View from Canyon Overlook, Zion Bryce Canyon. Dark Quaternary basalt on the left, National Park. with light Tertiary Claron Formation on the right.

We continued along UT-12, climbing up through the Red Canyon onto the top of the forested Paunsaugunt Plateau where we turned into the Bryce Canyon National Park (altitude 8,000 feet). We stopped at Sunset Point and as we walked towards the eastern rim of the plateau and looked downwards, the amazing multi-coloured pinnacles (or hoodoos) etched out of the Claron Formation were displayed before us in a large amphitheatre (Fig. 13.5). Despite its name, Bryce Canyon is actually a series of amphitheatres carved along the retreating eastern cliffs of the Paunsaugunt Plateau, the cliffs being formed by erosion of the Paria River and its tributaries that run along this side of the plateau. The Claron Formation consists of alternating horizontal layers of mudstone, siltstone, sandstone, conglomerate, limestone and volcanic ash laid down in lakes and rivers during the early Tertiary, about 55 million years ago. Over the past forty million years or so, tectonic forces have produced two near-orthogonal fracture systems within the Claron Formation, thus creating a cross- hatched pattern of joints. Weathering processes such as flash floods, freeze-thaw cycles and weakly-acidic rain have eroded the rock preferentially along these joints to produce tall fins and pinnacles of rock. Because of the alternating composition of the rock, differential erosion has produced knobbly shapes over the full height of each hoodoo.

Having feasted our eyes on the unique hoodoo formations in the mid-afternoon sunshine, we descended 500 feet into the amphitheatre down a steep talus slope on a 3-mile circular trail that allowed us to admire the kaleidoscope of colours and shapes at close quarters (Fig. 13.6). Some of the hoodoos had a cap rock of resistant limestone that protected the underlying rocks from erosion by running water, whilst in some areas vertical mud stalactites had formed from mud washed off higher levels. One of the sculpted rock shapes pointed out by our guide Tom apparently resembled Queen Victoria but this required a degree of imagination that a few of us clearly lacked. As we meandered through this unique landscape, the colours we saw changed in intensity with place and time. It was a spectacle we would never forget and a fitting end to yet another amazing day on the Colorado Plateau.

Fig. 13.6 Hoodoos in Bryce Canyon, from the Fig. 13.5 Bryce Canyon from Sunset Point. Queen’s Garden Trail.

Report and Photos by Norman Nimmo-Smith

25

The Colorado Plateau 2015

Day 14 Tropic to Grand Junction, Colorado

Our route on UT12 passed along the Cretaceous Tropic Shale (which reappears as the Mancos Shale further east) exhibiting noticeable coal seams. The road passed hoodoos of the Upper Jurassic Carmel Formation between Cannonville and Henrieville, before turning north-east and rising to 7610 feet through the Cretaceous rocks of the Kaiparowits Plateau. Descending a monocline at the end of the plateau the road returned to Jurassic rocks at Escalante. Climbing yet again to 9400 feet, and in places with drops of 1000 feet on both sides of the road we rounded the flat topped Boulder Mountain which is capped with Tertiary volcanic rocks that provide a supply of basalt boulders along the landslip we were now travelling over. Finally descending to the Fremont river and the Moenkopi Formation we entered Capitol Reef National Park, the last National Park of our trip. The name ‘Capitol Reef’ derives from the Navajo Sandstone, here 1000 feet thick, the domes of which are said to resemble the Capitol building in Washington DC. ‘Reef’ refers to the seemingly impassable cliff rampart of the and does not imply a geological carbonate reef. The fold is a dipping monocline probably resulting from a Precambrian reverse fault overlain with more ductile deposits (Fig. 1). It is 100 miles from north to south but barely 4 miles wide. Waterpockets form here where rainwater mixing with atmospheric carbon dioxide dissolves calcium carbonate cement between grains of a sandstone resulting in depressions in the rock. The Capitol Reef area represents nearly 200Ma of geology in 10,000 feet of sedimentary strata.

Fig. 1 Diagram of Waterpocket Fold (Capitol Reef National Park website, 05/05/2015,

We stopped at Panorama Point to view the Capitol Reef cliffs with the Henry Mountains behind, and to discuss the formation of the prominent talus slopes (Fig. 2). Driving on to the Grand Wash access point we walked then along the 2.2 miles of the Grand Wash which runs southwest to northeast across the middle of the fold, dropping 200 feet through Wingate Kayenta and Navajo Sandstones (although, because of the downlimb of the monocline, we were actually walking up the section). These three formations are Triassic in age, Orange Wingate cross bedded wind blown sandstones give way to Kayenta braided river sandstones which in turn are superseded by the massive Navajo sandstones, and together form the Glen Canyon group . At one point the shear walls rise 800 feet above the 20 foot wide floor (Fig. 3), and the immense cross bedding in the desert sandstones of the Navajo are spectacular (Fig. 4). As the name implies Grand Wash is subject to flash flooding. Incidentally Butch Cassidy is reputed to have had a hideout here.

Fig. 2 View from Panorama Point of front cliff edge of Capitol Reef showing vegetated talus in foreground now isolated from further sediment supply as cliff recedes.

26

The Colorado Plateau 2015

Fig. 3 View up the Grand Wash towards the Figure 4 Cross bedding in the Navaho Sandstone at narrow canyon. the narrows of the Grand Wash showing undercut caused by occasional flash floods.

Evidence of Uranium mining in the earlier Shinerump member of the Chinle formation can be seen at the start of the wash, although it was never commercially viable. Leaving the National Park, the last Park of our trip, we followed the Fremont River through dipping younger strata onto the badlands of the Morrison Formation. The route crossed the Cainesville Anticline and the syncline of the Henry Mountains Basin before returning to the Morrison Formation outcrop at Hanksville. Our route took us across the San Raphael Desert before we caught sight again of the infamous Book Cliffs reminding us that we were about to rejoin the I70, turning east for the run back to Denver, and that gave us an opportunity to stop at Rabbit Valley which we missed on our way out. Upper Jurassic Morrison Formation sediments in Rabbit Valley provided some examples of dinosaur fossils, left in situ by the Museum of Western Colorado after their excavations. Diplodicus vertebrae and Camarasaurus bones are exposed as well as plant material which showed up well in the late afternoon sun.

Report by Philip Ridley Photos by Averil Leaver

27

The Colorado Plateau 2015

Day 15 Grand Junction to Boulder

This was a day of travelling as we made our way back towards the Denver area. Most of our geology would be observed through the coach windows, but we had become expert in recognising the key formations of the Colorado Plateau that Tom pointed out to us (Fig. 15.1). The Interstate 70 follows the valley of the Colorado, accompanied by the railway, up and over the Rockies and this has been a tricky engineering project due to the complexities and instability of the geology.

As we had learned earlier in the trip the underlying Tertiary and Cretaceous rocks are a source of oil and gas. But in this area the fields are small and difficult to work. Tom recounted a tale of an adventurous scheme which had involved the explosion of an atomic bomb to release the oil and gas from the rocks. The products of this venture were found to be unusable as they were radioactive ! The well is now securely capped and further drilling prohibited. Travelling on we noted the change as we left the Colorado Plateau and entered the Rockies. The transition is marked by the Grand Hogback formed from the tilting of the Cretaceous Dakota Sandstones (Fig. 15.2).

Fig. 15.1 Passing by a mesa of the Mesaverde Fig. 15.2 View of the Grand Hogback from the coach Group sandstone, Wasach Formation siltstones and limestones, topped by the Green River formation.

We stopped for refreshments in Glenwood Springs. This town has grown around a thermal spring sacred to the Ute Indians. The spa town nestles in a valley, formed by the confluence of the Colorado River and the Roaring Fork River, in the (Carboniferous) Leadville Limestone. On our exit from the town we stopped to visit Glenwood Springs’ oldest cemetery which boasts the graves of ‘Doc’ Holliday and ‘Kid’ Curry (Fig. 15.3).

Fig. 15.3 View from Glenwood Pioneer Cemetery towards Glenwood Springs with hills of Leadville Limestone beyond.

The road followed the Colorado up Glenwood Canyon, the result of regional uplift and erosion during the Pleistocene glaciations, then on to a tributary, the Eagle River. This section has complex geology with unstable superficial sediments all contributing to the Interstate having an extended construction period of 13 years.

We stopped for lunch in Vail, one of many ski resorts in the area. Then on, over high passes, past Copper Mountain and through the Eisenhower Tunnels at over 11 000ft. As we journeyed we enjoyed the golden hues of the aspen but at higher levels were saddened by the number of dead larches which are suffering from the ravages of a beetle taking advantage of the warming climate.

28

The ColoradoColorado Plateau 2015 2015

As we dropped down the eastern slope of the Rockies we entered the zone of mineralization that has been a source of wealth for this area since the mid 19th century. We entered an area of faulting of the Berthoud Plutonic Suite, Middle Proterozoic granites, which have been mined for gold, lead, zinc and copper. We stopped in Georgetown (Fig. 15.4), a town that owes its existence to the ‘Colorado Mineral Belt’ but is now reliant on passing tourists.

Fig. 15.4 Main Street, Georgetown with hillside of Fig. 15.5 A gold mine near Black Hawk. Berthoud Plutonic Suite granites, its source of wealth, in the background.

Our driver, Todd, recommended an alternative route to Boulder over a new road recently constructed and paid for by the casinos of Central City. They had been losing trade as a backwater and are benefiting from increasing traffic flow through their city. The road was spectacular, winding and climbing up and around the Front Range Early Proterozoic gneisses and granites. Cities of the area, like Central City and Black Hawk, had thrived in the late 19th century on the rich mineral wealth but now have to find an alternative income although there was evidence of some gold mines still working (Fig. 15.5). The last part of our journey followed the canyon cut by Boulder Creek and led us by lakes created to hold water for the cities of the Plains around Denver. We were happy to reach the last hotel of our stay in the USA.

Report and Photos by Averil Leaver

29

The Colorado Plateau 2015

Day 16 Denver Hogback

The first location on our last day in the field found us alongside an impressive road cutting above the busy I-70. It has sliced through a prominent hogback formed from the hard Dakota sandstone.

We walked along a short geological trail, complete with helpful information notices, which followed a sequence of the Upper Jurassic Morrison Formation through to the Cretaceous Dakota Sandstone (Fig. 16.1). The contrasting colours and textures of individual beds represent a change in depositional environment from a coastal plain with rivers, deltas and sand-dunes to marine sediments. The varied colours are due to the different iron minerals derived from the weathering of the mafic minerals - magnetite, biotite and hornblende plus some carbonaceous deposits. Some claystone layers contained finely divided charcoal and small pyrite grains which suggested an ancient forest fire.

At the end of the trail we viewed the line of the hogback together with basalt outcrops on the far horizon. The mineral rich Dakota rocks in the provide important sources of water, oil, gas, uranium and pure clays. The clays are used for both brick Fig. 16.1 Road cutting through the Dakota making and ceramics. Hogback on I-70 looking north.

The eastern tilting of these rocks occurred during the Laramide Orogeny at the start of the uplift of the Front Range in the late Cretaceous Period (70 Ma)

A short drive then took us to the and the 300 million year old, very red, Fountain Formation. As the Ancestral Rocky Mountains were uplifted, 6,000 feet of Palaeozoic cover was eroded exposing the 1.7 billion year old gneisses of the Idaho Springs Formation to aerial erosion. The iron was oxidised to haematite and the red erosional debris deposited in huge alluvial fans to form the conglomerates and sandstones of the Fountain Formation. A natural amphitheatre of these red rocks has been developed into an impressive open air theatre, arts centre and restaurant.

We drove half a mile onwards to a nearby geological viewpoint, plus welcome picnic area, which gave us a superb view of the hogback along the Front Range (Fig. 16.2). The early autumn scenery was enhanced by patches of the scarlet-leaved Sumac shrubs and numerous butterflies. On the horizon could be seen a mesa of Palaeocene Green Mountain Conglomerate containing boulders of Precambrian metamorphic rocks which had been deposited at the foot of the rising Rockies. In the far distance we could make out the high-rise buildings of downtown Denver (Fig. 16.3).

Fig. 16.2 View of Dakota Hogback from Red Rocks Fig. 16.3 Green Mountain with Denver Park picnic area. skyscrapers in the far distance

For our final location at "Dinosaur Ridge", we followed a 1.5 mile walk along a de-commissioned road. This involved a traverse through the Dakota hogback with interpretive panels installed by the University of Colorado (Denver). In addition they have provided an excellent visitor centre which we visited near the start of the walk.

30

The Colorado Plateau 2015

The Morrison Formation exposed here represents a lush, wide and flat coastal plain which experienced periodic flooding and supported a rich ecosystem, including many species of dinosaur. The early 19th century fossil dinosaur finds were historically very important and are well illustrated in situ. Near the top of the Morrison Formation, on the eastern side, we saw a series of large, 40 cm diameter bulges interpreted as load casts of a Saurapod track made in the soft sand of a lacustrine beach (Fig. 16.4).

Moving around to the west side of the ridge, into the younger Cretaceous rocks, we marvelled at large expanses of symmetrical ripple marks formed in a littoral environment. There was much evidence of trace fossils in the form of invertebrate burrows and in other places we saw fossil microbial mats and impressions of driftwood and tropical plants. At "Crocodile Creek", interpreted as a 50 yard channel, there were remains of clam burrows and surface Fig. 16.4 Load cast of a large sauropod walking scratch marks thought to have been made by crocodiles as they over soft sand at the edge of a lake. swam near the bottom of the channel.

The highlight of the field trip was to view an inclined bedding surface of the South Platte Formation Sandstones (Dakota Group) which is covered in dinosaur track-ways and prints (Fig. 16.5). Both herbivorous ornithopods and carnivorous theropods are represented. Rounded, 3 toed prints are thought to have been made by Iguanodon, both adults and juveniles. Some 9 inch arrow shaped tracks were made by a dinosaur estimated to be about the size of an ostrich. Similar multiple tracks have been found elsewhere in the region and suggest a dinosaur migration route. It has been nick-named the "Dinosaur Freeway".

Fig. 16.5 Dinosaur trackway showing theropod tracks, narrow and arrow-shaped, approx 9in long, and ornithopod tracks, which are more rounded.

Report and Photos by Barbara Wood

31

The Colorado Plateau 2015

Day 17 Denver

From our overnight stay in Boulder we headed to Denver, Colorado's State Capital, to be dropped off at the Museum of Nature & Science (www.dmns.org). Their displays included: A Prehistoric Journey with many of the dinosaur skeletons being ones which we had seen encased in sediments in the field. A journey tracing the Evolution of Life, from single-celled organisms through to the present day, had some of us wondering how many of the American visitors actually believed what they were told at each of the stations. There were the usual stuffed modern - day animals and birds in relevant dioramas from around the world - perhaps lacking in imagination. The large Poisons Exhibition included a 'scientist' providing a demonstration of forensic science to investigate how a farmer and his family died in 1830. Agatha Christie's novel methods of poisoning were exhibited and proved to be a great favourite. A new, eagerly anticipated, Sherlock Holmes exhibition was in the final stages of preparation. On the Museum's Sky Terrace we were able to see solar-flare prominences and also sun-spots through various telescopes. In the city which boasts 300 days of annual sunshine, there was no problem with visibility. (Fig. 17.1)

Denver was founded in 1858 as a frontier town based on servicing local gold miners with gambling, livestock and goods. In fact the first permanent building was a saloon. Prior to this, the area had been used as a seasonal encampment for the Cheyenne and Arapaho Indians. The town was at the end of the 592 mile long Smoky Hill Trail, (www.legendsofamerica.com) - the immigrant and stage road from Missouri River to the gold fields, originally an ancient Indian trail. There were many deaths along this trail due to thirst and Indian raids. Some US characters associated with it include General Custer, Wyatt Earp and Buffalo Bill Cody. Fig. 17.1 View from the Museum looking West over Downtown Denver – the Mile High City

After lunch the coach set us off in Downtown Denver to wander around for 4 hours, with our city maps showing the coach pick-up point. The highlight for me was to discover an Irish Pub which served the best pot of tea in 2 weeks! At the end of the mall was the imposing Colorado State Capitol Building with its gold- plated roof. (Figs 17.2 & 17.3) As Denver is known as the 'Mile High City', the 13th step up to the State Capitol had a plaque telling us that this was the exact height above sea- level.

The Colorado Plateau has a height over 4000 feet, which meant that since we had left Heathrow airport our altitude at any time in the 2 weeks was above that and often much more. The rarefied and dry air of the Colorado Plain was a bonus to anyone suffering from painful joints.

We all arrived back at the coach on time and so headed to the airport. This covers an enormous area of 53 square miles - larger than Manhattan Island - with 6 runways. Denver Airport is the largest in the US with 54 million passengers a year going through 141 gates. The huge white-peaked fibreglass roof is reflective of the snow-capped Fig. 17.2 Denver’s State mountains and evokes Colorado’s early Capitol Gold plated dome history when Native American teepees were located across the Great Plains. Fig. 17.3 Looking up into Denver’s State

Capitol Dome

The nine hour flight home enabled us to reflect on what we had seen in the last fortnight.

32

The Colorado Plateau 2015

My highlights were:

 The alpine vistas with swathes of autumnal colours.  The wide open spaces and vast distances as we crossed prairie grasslands on long straight roads.  Colourful sediments revealed in the semi-arid climate..  Red Rock Country, familiar in the old cowboy films (Fig. 17.4).  The deluge in Monument Valley (Fig. 17.5)  Many low, smooth Laccoliths protruding from the plains like giant whales.  The iconic Meteor Crater of Arizona  The ride over the Grand Canyon in a small 8-seater plane  The extensive and concentrated dinosaur remains we saw at the Dinosaur National Monument and the many therapod tracks and remains we saw at other sites. (Fig 17.6)  Visiting the Navajo Nation. It was surprising to see the poverty of their simple townships in such a rich nation.  Ants and beetles with their long legs, an adaptation to prevent scorching their bodies!  Tarantulas crossing paths in front of us.  Beautiful Monarch butterflies around the towns, perhaps on the move south as it was September. Fig. 17.4 The Grand Wash canyon in Chinle Fm.  Many new birds, including four jay species and the lovely The sheer cliffs of Wingate & Navajo Sandstone Mountain Bluebird. Whilst the numbers of individual birds reach up to 800ft high and are 20ft apart in places were low there was a diverse range of species seen by the and cut through the Capitol Reef. birders amongst us. Butch Cassidy (Robert L. Parker) is reputed to have had a hideout here  The smells of the many aromatic shrubs and herbs including the swathes of grey Great Basin Sagebrush, Artemisia Tridentate, once used by Native Americans to ward off ticks.  The photogenic pinyon pines and juniper trees growing into unusual shapes and often strategically set against a stunning background (Fig. 17.7).

Many thanks to Tom and Janet for arranging our visit to such an amazing area. It must have been very difficult to decide which National Parks to visit but our itinerary was certainly packed full and what choices! Well done.

Fig. 17.5 The Mittens Monument Valley Buttes,

Fig. 17.6 Fractured dinosaur long bone at Rabbit Valley, Western Colorado

Report and Photos by Yvonne Cutt Fig. 17.7 Utah Juniper in Park Avenue, Arches National Park, Utah 33