Dan's Geology Field Trip

Historical Geology Field Trip: Dan Fosha, GEY 121 Fall 207; Prof. Trina Riegel

2007-11-21T14:19:00.001-08:00

This is the first post for my field trip for historical geology for the fall 2007 semester. The sites we will see will be from the Front Range of Colorado, and will focus on the layers that edge up against the mountain front. It is tightly based on a trip found in the book "Field Trips in the Southern Rocky Mountains, USA" published by the GSA. The trip starts in Boulder, at the intersection of Baseline Road and Highway 36. Exit Highway 36 and at the light, set your odometer to 0. Take a left at the light on Baseline. Here we go!

2.1 Miles: Here we have the first view of the Fountain Formation on the side of Flagstaff Mountain. The Fountain Formation is widespread in Colorado, and was formed from the erosion of the Ancestral Rocky Mountains. The Fountain Formation is made up of weathered granite from the easterly mountain range of the Ancestral Rockies, Frontrangea. The depositional environment was one of massive alluvial fans, perhaps like what we might see in Nevada today. The Fountain Formation is responsible for the major geological tourist attractions on the Front Range: Garden of the Gods, Roxborough State Park, Red Rocks Amphitheater and the Flatirons in Boulder.

It is composed of red sandstone and conglomerate, and some thin beds of mudstone. Within the rock, we find quartz, potassium feldspar, granite, and mudstone. The reddish color is particularly pronounced in the finer grained sediments, which we will see in detail in a few posts.

2.4 There is a panoramic viewpoint to the right. You might be able to make out some of the fault zones here. This is looking to the north. The hills in this picture are the tips of the broken rock layers peaking out from the surface, where they lay up against granite underneath.

3.6 First outcrop of weathered granite.

4.1 Stop here to your right at the bend. This is an interesting cross section. We'll scroll from the right to the left, from the parking area. The tilted layers are readily accessible here. To the right (east) are the youngest layers. We are facing north in this picture. This is the Fountain Formation. Look at the dip – it's about 50⁰ here.

This is pretty neat. Here may be an ancient soil, or a paleosol. Others think it is just Boulder Creek Granodiorite that weathered some before it was buried. The circle part that is red crumbles very easily. I found it difficult to call it rock. More importantly, look at the vein right in the middle. This is a quartz vein.

A close up of the weathered granite.

Here is another shot further to the southwest of more veins.

The Boulder Creek Granodiorite is in full force here, showing typical granitic weathering patterns. The brown color is from modern day weathering.

A close up of unweathered (relatively) Boulder Creek Granodiorite.

Here we are looking at the far southwestern end of the outcrop. The Granodiorite is to the left and to the right, the rock becomes a bleached red color and crumbles easily. Scientists think that this is an indication of Paleozoic weathering.

Go back down the hill. You can stop at the panoramic viewpoint if you like again. It is at mile 5.8.

7.5 Turn left on 6^th street. Follow it through the neighborhood to Canyon and take a left.

7.7 Turn right here after the Watershed School, and then an immediate left into the parking lot of Settler's Park. Cross the bridge and walk up to the rock formations here. There is supposed to be a small quarry here, but I didn't find it. I did look at rocks which I think are interesting. Look at the dip in this next picture. It's 90⁰ or more. It is a reverse fault. In some places along the Front Range, older granitic rocks have been pushed over younger sedimentary rocks.

In this park we see the Fountain Formation start to intergrade with the Lyons Sandstone. I think this pink layer here is the Lyons Sandstone.

Here is a close up of the pink sandstone.

After looking around, go back to the parking lot.

7.7 Leave the parking lot, and then turn left on Canyon.

9.4 At 28^th street, turn right. It becomes Highway 36. Keep going

20.9 At CO 121 (Wadsworth Boulevard), exit and go south.

31.1 At I-70, go westbound.

41.1 Take the Morrison exit. Then turn left onto Hogback Road, all the while watching for the signs to Red Rocks Park.

42.9 Take the first entrance to Red Rocks Park. Turn right and go all the way up to the Top Circle parking lot for Red Rocks and the Visitors Center.

43.7 Keep going straight past the parking lot on the left for Red Rocks Trail.

44.1 The road goes through a fun arch tunnel cut.

44.4 Park here.

To the northwest look for a marker stuck in the rocks. It indicates the contact boundary between the Idaho Springs Formation and the Fountain Formation. First notice that the Granite here, to the right, doesn't show as much weathering as the Boulder Creek Granodiorite did earlier in our trip. Then to the left, see the obvious conglomeritic nature of the Fountain Formation.

A close up of the Fountain Formation's conglomerate tendencies. I think this is at the contact point too.

Now walk over to the signs for the visitor center, between the two giant rocks sticking out of the ground. To your left as you walk will be Creation Rock, and then farther to the south, forming the south side of Red Rocks Amphitheater will be Ship Rock. Both of these rocks show the characteristic alternating pattern of the Fountain Formation between chunky paler, conglomerate and dark red finer grained laminated redbeds. Here is Ship Rock.

And here is Creation Rock, the other frame of the Amphitheater. Notice the alternating layers?

Here is a close up look at the layers.

Inside the visitor's center are some neat displays. This one is of a fossilized palm frond from the Cretaceous Era. They also had some Dinosaur tracks, but I'll show you some better ones later on.

Of course, you have to look at the 'natural' Amphitheater that was built here. Where the stage is now was a pile of boulders that had to be blasted away. This picture is interesting too in that it shows the other layers of sedimentary rocks that are tilted up against the Front Range. As we look east here, the younger rocks are farther away. The big ridge dotted with trees is the Dakota Hogback. To the left in the back of the picture is Green Mountain, a very young pile of conglomerate. You can just make out the Denver skyline to the right of Green Mountain.

Go back to your car when you are finished looking around.

44.4 Go back down the hill.

44.9 Turn left where it says 'Geologic Marker'.

45.2 There is a cul-de-sac here. Park in the lot, and go up the concrete stairs to the southeast. There is a neat sign here that explains the geology of this area. It has a similar view to that of the last picture. Here is a close up of the diagram.

45.5 Go back to the road out of the park and take a left.

45.9 Watch for a weathered old sign indicating the Fountain Formation (how convenient!)

46.1 Pull off here, where there is a sign for the Lyons Sandstone. Here is a close up of it. The sign is to the right of this picture. It's taken looking north. Supposedly this is the coarse grained version of the Lyons Sandstone. Bigger grains, that are almost conglomerate sized, indicate that this rock can not be the result of Aeolian, or wind blown sedimentation. I only saw some fine grained sandstone with some neat cross bedding.

Continue down the hill.

46.2 Another weathered sign, this time for the Lykins Formation.

46.5 Junction of West Alameda (Red Rocks entry road) and Hogback Road. Go straight across.

46.7 Stop here; just pass the small metal shelter. Walk back down the road to the shelter and display. The display features fossilized dinosaur bones in the famous Morrison Formation. The darker color makes them fairly obvious. Many of these bones were destroyed when Alameda Parkway was built, but it is likely that there are more bones farther into the hillside. All in all, there are 109 bones visible along this outcrop. The dark stained spot in the center is a pelvis bone, I think.

The Morrison Formation is mostly quartz and a little feldspar. The cement is "ferroan dolomite" with some kaolinite mixed in for good measure. The direction of 'transport' or deposition of the sandstone is to the right side of this photo. There was probably a river near here and the bones, from a dinosaur already dead, were moved about in the water during a flood, and later deposited in a floodplain. So we are probably looking at a sandy streamside. Supposedly, to the left of the bones, the sand is a little coarser, as they stopped bigger sand grains from moving along. The bones are not cracked on their surface, so they were probably buried quickly, probably by sand dunes.

Here is a photo of the upper part of the Morrison Formation. This part is not as resistant to weathering as the lower part is where the bones are located.

Walk farther up the road to the next interpretative sign, the 'Brontosaurus Bulges'. The only way geologists have found to explain these small bulges in the rock layers is that they are the tracks of Apatosaurus (aka Brontosaurus). These dinosaurs were so heavy that they compressed the soil, making a deep impression, and the track was subsequently lithified.

At point you can continue walking up the hill to see all the signs, or drive to the parking area on the other side and walk back up the hill. I will continue in sequence up Alameda Parkway.

As we walk up the hill, we meet younger rock layers. Here is a layer of ash that fell when a Cretaceous volcano erupted in central Colorado. It is somewhat protected in this case. You can see the thin layer go up to the right of the case.

Here is a close up of the ash layer.

Going over the hill, there is a neat sign that shows how the Denver basin was formed and how petroleum was trapped in it.

And here is another one that has a good diagram of reverse faulting along the Front Range.

As we continue down the hill, we get to a younger rock group called the Dakota Group. It is mostly sandstone. Here is a picture of Dakota sandstone, the rock that forms the well known hogback that runs from Colorado Springs to Fort Collins. If this doesn't just say to you "the West", what else do you need, a cowboy hat?

7.1 Here is a bedding plane in the Dakota Group with ripple marks. It's on the east side of the hill, continuing down from where we were. It was likely formed in a 'quiet, intertidal zone'.

Next are some trace fossils, which are burrows and tracks of worms and crustaceans. These are very similar to what we see in modern day tidal flats.

47.3 The grand finale, the Dinosaur Ridge Track site. These dinosaur tracks are located in the Dakota Group. They are very famous, and I think they are better than the ones on the Comanche National Grassland in Southeastern Colorado. In this next photo we are looking up at a 30⁰ angle to the west.

Note that these tracks are colored with charcoal so that they are easily visible. They were discovered in 1937, but not seriously examined until the 1980s (What were those people at Mines doing all that time?) There are two track types here. Both of them are tridactyl, meaning that they were three-toed. The larger footprint was made by a larger dinosaur, something like an iguanodon, which is an ornithopod dinosaur. In the photo above you can see two different sizes of the same type of track. The small ones were probably made by juvenile iguanodons. This picture below, from the website: HUhttp://www.duiops.net/dinos/iguanodon.htmlUH, looks like it could be right from this site in Colorado.

The smaller tracks were made by an ornithomimid dinosaur, maybe ornithomimus, which looked similar to a modern day ostrich.

At the bottom of the hill is a gift shop that has many books and materials about the track site. It also has a lot of dinosaur paraphernalia and other educational materials. If you are interested, there is another dinosaur track site just south of Golden. I didn't have time to make it there, but it is supposed to be very good. Just south of 19^th street and west of US Highway 6, there is a turn off for the 'Triceratops Trail'. I hope you enjoyed this brief look at some of Colorado's geology.

Sources:

Chronic, Halka; Roadside Geology of Colorado; Mountain Press Publishing Co., Missoula, MT 1980

Lockley, M. G.; A Field Guide to Dinosaur Ridge, A Publication of the Friends of Dinosaur Ridge and the University of Colorado at Denver Dinosaur Trackers Research Group, 29 p. 1990

Nelson, Eric P., Erslev Eric A.; Field Trips in the Southern Rocky Mountains, USA; Geological Society of America, 2004.

Weiner, Robert J. and Haun, John D.; Guide to the Geology of Colorado, ed. Geological Society of America, 1960.

Thanks!

2007-04-29T12:57:00.000-07:00

That's it! I hope you enjoyed this short tour of the some of the geology around Denver, and thanks for viewing.

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Sources:

Fossils in Schlessman Hall, Pamphlet, Denver Public Library 12/03/5C

Guide to the Geology of Colorado, ed. Weiner, Robert J. and Haun, John D., Geological Society of America, 1960.

Murphy, Jack A., Geology Tour of Denver’s Capitol Hill Stone Buildings, 1997, Historic Denver, Inc., Denver, Colorado, 96 p.

Murphy, Jack A., Geology Tour of Denver’s Buildings and Monuments, 1995, Historic Denver, Inc., Denver, Colorado, 96 p.

Plummer, et al. Physical Geology, 11th edition. McGraw-Hill Higher Education 2007

http://www.cliffshade.com/colorado/index.htm

Roxborough State Park and Environs

2007-04-29T11:05:00.000-07:00

On to Roxborough State Park which showcases four important Colorado geological formations. Starting from youngest to oldest they are the Dakota Sandstone, the Lykins Formation, the Lyons Sandstone and the Fountain Formation. A good cross section is found on this page.

Here are a couple pictures of Dakota Sandstone, the first layer in the famous Front Range hogback. Notice in this first picture the oak thickets and juniper on the flank of the hogback. I'm not sure why the plants prefer this environment on the Dakota, but this phenomena seems to be consistent along the Front Range.

The Dakota sandstone is beach sand, and often has ripple marks, and I think the source for the sand was the ancestral Rockies, as massive rivers poured out of them and eroded them away. Dakota Sandstone was formed during the age of Dinosaurs, and so fossils are relatively abundant here. This part of Colorado was a giant shallow inland sea at the time when the sand was deposited.

It was then uplifted during the Laramide Orogeny, which is a technical way of naming the time when the mountains we have today in Colorado were first created. All of these rocks here in the park form the limb of a syncline that dips to the east.

Next over is the Lykins and the Morrison Formation. The Lykins formation is just by the parking lot, and is composed of colonies of fossilized blue-green algae, probably similar to the health food supplement. These fossils are called stromatolites, and they form thin beds in the rock.

During the time when the Lykins Formation was formed, Colorado looked like Iraq, an area of shallow coastal mud flats and arid low lying inland areas. I didn't get a good photo of the Lykins, so I will offer you this one instead from the website of the Denver Museum of Nature and Science. Click on Lykins to see what the stromatolite layers look like. Here's an even better one.

Here in Roxborough, the Morrison Formation supports a healthy grass population, and isn't easily seen. I think the Morrison Formation is underneath this meadow here, as shown in the photo above.

The Lyons sandstone has grains that are more rounded compared to the Fountain Formation. Supposedly Ponderosa Pine and Kinniknnik are common here. This is just behind the upper parking lot.

Lyons Sandstone was formed during a time when the area was covered by coastal sand dunes but still had major rivers flowing through, perhaps like Egypt with the Nile or Iraq with Euphrates/Tigris system.

The Fountain Formation is easily identified by the relatively large, sharp grains of sandstone mixed with pebbles of quartz and feldspar. Also unique are the lichens that seem to prefer it as a substrate, shown in the second photo.

During the formation of the Fountain Formation, there was a lot of erosion from rivers that flowed out of the Ancestral Rockies, the mountain range that was here before the Rockies we know of.

Directions (from Highway 85/Louviers):

32.5 take ramp to Titan Parkway. Go west. Stay on road towards Roxborough (follow signs)

39.2 Dakota hogback approaches.

39.6 Road goes through Dakota Sandstone.

42.1 Roxborough State Park.

Across the Alluviums

2007-04-29T08:37:00.000-07:00

From here, it’s time to go on an excursion. I like to hike in Roxborough State Park, so we’ll travel out there and look at the geology along the way. As we go, we'll drive across the alluviums that sit underneath the metro area. All the alluviums that form the surface geology of the Denver area are outwash from the Colorado Rockies that still rise above the plains, not the ancestral Rockies, which are long gone.

This diagram, copied from "Guide to the Geology of Colorado" shows a cross section of the alluvial terraces in the Denver area. I-25 and the South Platte, for example run in the little trough on the far left of the diagram, so as we view the cross section we are facing south. The type is too small to be scanned legibly, but to get the idea, know that each terrace is an alluvium from a different time era. In general, the younger alluviums are to the left, and the older ones are to the right. Bedrock (not shown on the diagram) can be found peaking through the alluviums, like at Roxborough, or to the far right against the mountains, like the Flatirons in Boulder.

This first picture is the corner of Kalamath and Colfax. Piney Creek Alluvium(1500 years old or so) is underneath the street here.

This next picture is at 2nd and Kalamath. A mammoth tooth was found here. Fossils of extinct mammals are often found in alluviums in the Denver area.

This picture is perhaps what the alluvium looks like, a mix of gravel and sand.

Here is the South Platte, taken from Santa Fe going south in the Littleton area. Post-Piney Creek alluvium is along the main channel of the river. Post-Piney Creek alluvium is an alluvium similar to Broadway alluvium, but Broadway alluvium is much older, about 10,000 years old or so.

Here is some more Eolian sand blown from the South Platte River. Look at the rabbitbrush and sandsage in the second picture, telltale signs of sand beneath the soil.

This picture, looking to the west of Highway 85 (Santa Fe), shows terraces of the South Platte.

This is a picture of Broadway alluvium on the road to Louviers. We are getting closer to East Plum Creek.

This alluvium here is the Louviers alluvium, and comes from weathered Pikes Peak Granite.

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Directions (from Library):

Continue on 14th Avenue east.

5.2 left on Lincoln

5.3 left on Colfax

6.1 left on Kalamath: Post-Piney Creek Alluvium

Continue south on Kalamath.

7.7 2nd and Kalamath. Mammoth tooth found underneath.

Continue on Kalamath. Kalamath becomes Santa Fe (Highway 85)

12.8 South Platte on right. Continue on Santa Fe.

20.9 Sand dunes and shrubs on left.

21.2 Terraces of the South Platte on left.

25.7 turn right to Louviers

26.9 Broadway Alluvium on right. Follow road across bridge and into Louviers. Stay on road to the left out of town. Road goes to left again back towards creek.

28.4 Louviers alluvium. U-turn. Go back to Highway 85

30.3 turn left on Highway 85.

Denver Public Library

2007-04-26T09:19:00.000-07:00

I spend a lot of time at the Denver Public Library. I think it rivals any other public library in the country. The collection is vast and the checkout terms are generous. The Central Library Branch is also an interesting place to visit for the stones it is made from.

The old wing, shown in these pictures is made from Salem Limestone from Indiana, and the dark green border on the bottom is granite reportedly from Austria. Here is a closeup of the green granite. Note the color is washed out because of the sun.

On the new wing there are two different types of limestone. The beige limestone on the south side of the library comes from the area around the town of Solnhofen, near Eichtstatt in Bavaria, Germany. This limestone is also used in the floor of the ground level floor. It is easy to see large ammonites, which are kind of like nautilus shells, coiled around themselves, and up to 8 inches in diameter. These fossils date back to the Jurassic era, about 150 million years ago. These fossils were formed when the critters died a lonely death in the muddy lagoons of long ago, when they swam into the wrong area and asphyxiated from a lack of oxygen. Their shells were buried and then fossilized.

The other limestone is found on the northwest
side of the building, and forms the trim on the floor.The green limestone is from Frankfurt, Germany and contains fossils as well. These are called belemnites, and they have spear-tip shaped shells. They are ancient relatives of squid and octopi. One library clerk told me that many geologists and naturalists visit the library to look at the floor just to see the fossils.

I walked around the library and found that the red surfaces and some of the green surfaces are just painted concrete.

The presence of the fossils, and the smooth surface of the limestone indicates what is true stone and what is concrete.

The base of the pillars is made from Stony Creek Granite, which comes from Massachusetts. It is a Proterozoic-age granite gneiss, and you can see the big crystals in the photos here. The white is quartz, the tan crystals are orthoclase
feldspar, and the black is biotite mica.

Directions (from RTD Plaza):

Turn right on Colfax.

4.3 left on Glenarm. Make a U-turn because of construction. Right on Bannock. Left on 14th Avenue.

5.1 Denver Public Library

RTD Plaza and the 16th Street Mall

2007-04-26T09:02:00.000-07:00

I often ride the bus to work, and I usually pass the Civic Center Station when I do. RTD Plaza is the open area on top of the station, and it anchors the end of the 16^th Street Mall. The flagstones on the pathway are cut from two different types of granite.

The red granite is from Larimer County, and the gray granite is supposedly from Massachusetts, and the dark gray granite used to make these benches is from Minnesota.

Directions (from Colorado National Bank):
Continue southwest on 17th street.
3.7 right on Broadway
3.9 right on Cheyenne Park.
Park. RTD Plaza is behind you across Broadway

Denver Federal Court House and the bank.

2007-04-25T23:49:00.000-07:00

On my way to work, I usually pass the Byron White Federal District Court House on 18^th and Stout. This building used to be the post office, but after renovations in 1992 it became the court house. The building is constructed from Yule marble, and the original marble had suffered serious weathering due to downtown air pollution. Since the Yule marble quarry reopened in 1990, all the panels were replaced and the building you see now is from marble that has only been exposed for 15 years.

The sculptures of the big horn sheep you can barely make out are made from Salem limestone from Indiana, a type of the famous Indiana limestone used to make the Cathdedral walls.

Just across from where I work is the former Colorado National Bank Building. This building is all Colorado Yule Marble inside and out, with the exception of the base of the building, which however, is some type of granite. The buildings look somewhat alike, don't they?

Directions (from Fisher Mansion):
Continue north on Logan.
2.2 left on 18th.
2.6 go to the right to stay on 18th street
Old Post Office
3 left on Arapahoe
3.1 left on 17th street
Colorado National Bank

Back to the map for downtown

2007-04-25T23:40:00.000-07:00

Next we go into downtown, where the foundation of the area changes some. These buildings here are built on the Broadway alluvium, and for some, the foundations go down into the bedrock Denver formation. Deeper into the Denver Formation is a major aquifer. It is an important water source for communities not tapped into the elaborate Denver Water Board system.

Looking at the map again, we can see the change in color as we go from ‘ed’ to ‘asa’, which is the Broadway alluvium, and Broadway alluvial terrace.

This is a river terrace cut, and is the old flood plain of the South Platte. The boundary is pretty clear as you drive north along Lincoln just pass Cherry Creek. There will be a hill on your right side from there at Speer until you pass 20^th Avenue. The lower part of your left is the Broadway Terrace.

In the Denver area Broadway alluvium is about 6-12 mm thick and consists about equal parts sand and gravel. The gravel is made up of granite, pegmatite, quartz and small amounts of gneiss and schist, and there are beds of clay mixed in various places.

The next few buildings are built on top of this alluvium.

Fisher Mansion

2007-04-25T23:05:00.000-07:00

Two blocks from the Cathedral, on 16th and Logan is a mansion that I find interesting to look at as I go to work. The Fisher Mansion is mostly made of an unknown sandstone. To me the yellowish color is unusual for Colorado.

The columns supporting the fence are made of Silver Plume Granite. This gray granite is one of Colorado’s oldest exposed rocks, at around 1,400 billion years old and is found near Silver Plume on I-70.

Here's a close up of the granite.

Directions (from Cathedral):

Continue north on Pennsylvania

1.9 left on 16th.

2 right on Logan

Fisher Mansion on southeast corner of Logan and 16th.

Cathedral of the Immaculate Conception

2007-04-25T21:49:00.000-07:00

Our next stop is the Cathedral Basilica of the Immaculate Conception. This Catholic Church was built from 1902-1912 on the corner of Colfax and Logan. The outside of the building was built with Indiana limestone, which is a common building stone for monumental style buildings, including the Empire State Building. It was also used for the Episcopal Church just down the street. It is a freestone, meaning there is no grain or lines, so it can be cut in any direction, and be cut with a lathe.

The altar piece in the center of the photo is made
from Carrara marble from Tuscany, Italy.

This is the marble that was used for famous sculptures by Michelangelo and other Italian artists.

The trim in the rest of the chuch is made from Yule Marble, taken from the quarry near Aspen. Yule Marble was, long ago, merely Leadville Limestone, until the heat from Tertiary age intrusions in the Elk Mountains, were it is found, baked it into marble.

The base of the outside appears to be a type of granite from the Aberdeen Quarry in Gunnison.

Directions (from Milheim):

U-turn. Go north on Race.

.4 Turn right on 17th. Stop at St.Mark's for coffee and almond croissant.

.5 Turn right on Vine. Go south on Vine

.7 Turn right on Colfax.

1.8 turn left on Pennsylvania. Turn into parking lot on left.

Lyons Sandstone and the Milheim House

2007-04-25T21:24:00.000-07:00

The next stop is just down the street at 1515 Race, which is the Milheim House. While made mostly of brick, it does have some nice sandstone trim.

This sandstone was called Manitou sandstone by builders , but geologists refer to it as Lyons Sandstone. This sandstone was quarried from Red Rock Canyon, which is just south of the Garden of the Gods. The quarry is now part of Colorado Spring Open Space, and you can hike around in the quarry and see where they cut the stone.

Here's a photo I did not take, and found on the web of Lyon Sandstone in Red Rock Canyon.

This layer of sandstone sits above the Fountain Formation, which I will write about later when we get to Roxborough State Park. Lyons Sandstone in the Colorado Springs area is about 176 feet thick, in a ledge that juts out of the ground. The size of the outcrop here allowed builders to cut big pieces for Denver buildings.

The layer was at one time horizontal, but now is almost vertical, as the entire layer was uplifted with Rocky Mountains and bent, in a ductile manner. This limb of a syncline was eroded away at the top, where it sticks out from the ground.

Here are the grains:

Both the Milheim and the Raymond Mansions are near St. Marks Coffeehouse, which I often visit for a fresh pastry.

Directions (from Castle Marne):

Go south on Race.

.2 Milheim on right.

Wall Mountain Tuff and the Raymond Mansion

2007-04-25T20:56:00.000-07:00

The first stop on tour is just around the corner from my apartment. I usually ride my bike by this house on the way to work. The building we’ll look at is the Raymond Mansion, also called Castle Marne by the owners who operate it as a bed and breakfast.

This building is one of the best examples in Denver of the use of Castle Rock rhyolite, which is the trade name for Wall Mountain Tuff. Wall Mountain Tuff was deposited about 36 million years ago all over Colorado and came from a huge volcanic explosion, bigger than Mt St. Helens. It erupted from the area where the present day Sawatch range is. The pyroclastic flow was mostly ash when it got to the area around Castle Rock, and when it cooled it solidified into a rock layer about 30 feet thick. It form caps on some of the buttes in the area, and has been quarried for about 125 years in Douglas County.

This house is just around the corner from me at 1572 Race. Notice the hitching post outside.

The older houses still have them, and they are usually made of sandstone. This is a closeup of the sandstone grains.

Directions for this leg: (Units in miles)
Start at Vine and Colfax.
Go north . 1 on Vine and turn left on 16th.
.15 Go west and turn left on Race.
Raymond Mansion on corner (Castle Marne)

Capitol Hill Area

2007-04-19T22:38:00.000-07:00

I live on Capitol Hill in Denver. Capitol Hill has its own interesting geology, as well as some of the most architecturally interesting buildings in Denver and they were built with readily recognizable rocks. First, I'll talk about Capitol Hill itself, and then some of the great buildings you can find in the area.

Capitol Hill is located east of the South Platte River and north of Cherry Creek, in the South Platte River Basin. The high point of Capitol Hill is in the Denver Botanic Gardens, near 10th Avenue and York Street, at about 5370 feet. The neighborhood is built on Eolian stabilized dune sand, probably blown out of the banks of the South Platte and Cherry Creek flood plains.

A very good map of the surface geology of Denver can be found at the link below. The crosshairs is right on downtown, and Capitol Hill is to the right, where the color changes to yellow. The yellow is all sand. Just to the left are the South Platte and Cherry Creek. One can see how the dune sand is only on the southeast side of Cherry Creek and the South Platte, and this suggests that it is wind blown sand, as the predominant winds blow from the northwest as they warm and decompress coming down from the neighboring Rocky Mountains. Notice how the stretch of dune sand that Capitol Hill is on trails out to the southeast from just below the confluence the South Platte and Cherry Creek. The grains decrease in size from the northwest, as the wind loses strength in that direction and can't carry the big grains as far.

http://pubs.usgs.gov/mf/2001/mf-2347/

The ‘ed’ in the yellow is the stabilized sand dunes. Cherry Creek reservoir is the ‘w’ surrounded by blue.

There’s an older map here:
http://store.usgs.gov/mod/images/i731p.gif

I didn’t find any outcrops where this sand might be. However, researchers describe it as being grayish, yellowish quartz sand with some clay and silt. The dunes themselves were generally flat, with some degraded parabolic dunes (arms to the northwest).

In other places in Colorado that are not so heavily developed, one can spot likely sand dunes by the presence of sand sage (Artemisia filifolia).

Sand deposits on Capitol Hill are no more than 6m thick. They sit on top of the Broadway Alluvium, which I’ll talk about in a bit. The sand dunes here are generally leveled before construction begins.

Artemisia filifloia

Photo by Mary Ellen Hart
http://www.forestryimages.org/browse/detail.cfm?imgnum=1358139

Intro to the Report

2007-04-19T22:35:00.000-07:00

Welcome to my Field Trip report for Geology 111, taken from Colorado Community Colleges Online.

For this report, I thought I would give you a tour of some of the geology highlights I see in my daily life here in Denver combined with a hiking excursion out to the foothills.

Here we go!