EOCENE AND OLIGOCENE MAMMALS FROM THE GRAVELLY RANGE OF SOUTHWEST MONTANA

Our first paper on work that several of us are doing in the Gravelly Range, southwestern Montana, was just published in a special issue of Paludicola, Scientific Contributions of the Rochester Institute of Vertebrate Paleontology. This issue contains papers in honor of James Gilbert Honey, a paleontologist and stratigrapher who focused on the Cenozoic, particularly the paleontology/evolution of camels and the Paleocene’s Fort Union Formation geology and paleontology. We’re pleased to have our work included in this volume! You can find our entire paper at:

Rochester Institute of Vertebrate Paleontology – Paludicola:

Donald Lofgren, Debra Hanneman, Jackson Bibbens, Liam Gerken, Frank Hu, Anthony Runkel, Isabella Kong, Andrew Tarakji, Aspen Helgeson, Isabel Gerard, Ruoqi Li, Sihan Li, Zhihan Ji. 2020. Eocene and Oligocene mammals from the Gravelly Range of southwestern Montana. Paludicola 12: 263-297.

Our paper’s abstract is: High elevation outcrops of Tertiary strata in the Gravelly Range of southwest Montana yield late Uintan to Whitneyan vertebrates that comprise five mammalian assemblages; Rapamys Site, Black Butte Low, Teepee Mountain, Black Butte High, and Lion Mountain High. The Rapamys Site and Black Butte Low are late Uintan or early Duchesnean. Two new species are present at the Rapamys Site (the carnivore Lycophocyon tabrumi and the rodent Pareumys muffleri). Small mammalian assemblages from Teepee Mountain and Black Butte High are late Duchesnean-early Chadronian and Chadronian, respectively. The most diverse assemblage is from Lion Mountain High, which is correlative with Whitneyan faunas from Wyoming, Nebraska, and South Dakota. The Whitneyan age of the Lion Mountain High assemblage is further age constrained by an underlying tuff with a weighted mean 40Ar/39Ar age of 31.7 +- 0.02 Ma and an overlying basalt flow with a K/Ar age of 30.8 +- 0.7 Ma. Paleogeographic range extensions into Montana for Lion Mountain High taxa include Diceratherium tridactylum and Oxetocyon cuspidatus. The taxonomic composition of the combined Rapamys Site/Black Butte Low mammalian assemblage is most similar to those from southern California, rather than geographically closer assemblages found in Wyoming and Utah. Comparison of undescribed middle Eocene mammalian assemblages from southwest Montana to those from southern California will further elucidate the middle Eocene Montana-California paleobiogeographic affinity.

Our geology paper on this area is soon to follow….

Devil’s Slide and A Jumping Fox

Devil’s Slide, a part of Cinnabar Mountain, is located about 3 miles north of Yellowstone National Park’s northern boundary and about 7 miles northwest of Gardiner, Montana. The “slide” or red streak on Cinnabar Mountain is developed in Triassic red beds.

Whenever I drive to Yellowstone National Park’s northern gate, I pass by the Devil’s Slide. It seems that the slide is my gate keeper to the park, and it is always fun to see it in all our different seasons. And once again, during a chance conversation in the park, I was asked about the geology of Devil’s Slide. Because of that conversation, I thought that I’d spend some time blogging about the slide’s geology.

Devil’s Slide is a part of Cinnabar Mountain, which contains steeply-dipping to overturned Paleozoic and Mesozoic strata. Cinnabar Mountain is fault-bounded on its north side by the Gardiner Fault, a north to northeast dipping reverse fault zone. At Cinnabar Mountain’s north end, the Gardiner Fault juxtaposes Archean crystalline rock (now partly masked by Tertiary intrusive rocks and Quaternary glacial sediments as shown on geologic map snapshot below) on the fault’s northern, up-thrown side against Paleozoic strata on its down-thrown, southern side. The Paleozoic-Mesozoic strata in Cinnabar Mountain are contorted because of drag associated with the Gardiner Fault.

Cinnabar Mountain and Devil’s Slide area as a snapshot from the Geologic Map of the Gardiner 30’x60′ Quadrangle, South-Central Montana (Berg and others, 1999, Montana Bureau of Mines and Geology Open-File Report 387). Map symbols on Cinnabar Mountain are: Mm = Mississippian Madison Group, PMs = Permian-Mississippian rocks, Psh = Permian Shedhorn Sandstone, JTrs = Jurassic-Triassic rocks, Kk = Lower Cretaceous Kootenai Formation, Kmfr = Upper and Lower Cretaceous Mowry Shale through Fall River Sandstone.

According to Marius Campbell and others (1915, p. 92), “Cinnabar Mountain was named in the early days, when the bright-red streak that marks it from top to bottom was supposed to be due to the mineral cinnabar, a red ore of mercury.” (From: Guidebook of the Western United States: Part A – The Northern Pacific Route, With a Side Trip to Yellowstone Park, U.S. Geological Survey Bulletin 611). We now know that the bright red streak is not cinnabar (a brick-red form of mercury sulfide), but the area of red in Devil’s Slide is actually a set of Triassic age red beds that mark widespread continental deposition and limited marine incursions throughout the Rocky Mountain region. The red beds in this case get their color from the oxidation of iron-rich minerals contained within the rocks.

And now for the jumping fox and its association to my Devil’s Slide discussion – as I said previously in this blog, the conversation that I had with a fellow-park goer a few days ago brought about my blog on Devil’s Slide. My conversation about the slide happened while I was watching a fox hunt rodents in YNP’s Round Prairie, a gorgeous meadow near Pebble Creek Campground in the park’s northeastern area. The female fox hunted for hours that morning, and several photographers and myself were enthralled with her hunt. The light snowfall of the night before accentuated the bushy fall coat of the fox and gave the hunting scene great color contrast. Here are are few photos from the hunt:

Round Prairie fox with her gorgeous fall-winter coat.
Round Prairie fox on the hunt.
Round Prairie fox on her hunting jump.
Round Prairie fox finishing her hunting jump.

Tolting Around Pseudocraters at Lake Myvatn, Iceland

The Lake Myvatn area, located in northeast Iceland, has an amazing, and truly beautiful, volcanic landscape. This area lies within Iceland’s North Volcanic Zone, which is a part of the Mid-Atlantic Ridge – the spreading rift between the Eurasian and North American plates that slices through Iceland. Lake Myvatn is the fourth largest lake in Iceland, and is quite shallow, with the deepest part being only about 4 meters. This area is also renown for its wetlands and birdlife, with the lake’s numerous bays and its outlet to the north-flowing river Laxa being host to a multitude of birds.

Lake Myvatn, viewed from the lake’s eastern side.
Basaltic landscape in the Hofdi area, on the southeast side of Lake Myvatn. Hofdi is a rocky promontory into Lake Myvatn that affords excellent bird watching.
Lava pillars in the Kálfastrandavogar area, southeastern Lake Myvatn.

My favorite experience at Lake Myvatn was riding an Icelandic horse around the pseudocraters in the Skútustaðagígar area of Lake Myvatn (southwestern part of the lake). Pseudocraters are unusual in that they are rootless volcanic cones that formed in this area about 2300 years ago when basaltic lava flowed over the water-logged lake sediment, resulting in the cones being built from steam exploding through the lava. So -not only did I want to see pseudocraters, but I also wanted to lean how to tolt because this is a natural gait exclusive to Icelandic horses. According to Riding-Iceland.com,

“the Tölt is a natural, fluid gait of the Icelandic Horse, during which at least one foot always touches the ground. Foals often tölt in pastures at an early age. The tölt is an extraordinarily smooth four-beat gait, which allows the rider an almost bounce-free ride, even at 32 kmh (20 mph). “

I contacted Safari Horse Rental (located just off the main road in the Skútustaðagígar area) and set up a two hour ride. Gilli was my guide, and he took me through mostly private land to both look at pseudocraters and to teach me how to tolt. It did take me awhile to understand how to let my horse know it was time to break into the tolting gait, but when we both got it figured out, wow! what a way to see pseudocraters! I’d urge anyone who loves to ride horses to try this!

The start of the pseudocrater exploration ride at Safari Horse Rentals!
A pseudocrater looms ahead of us. The pseudocraters are typically composed of tephra, scoria, and splatter that resulted from basaltic lava flowing over water-logged lake sediments forming steam eruptions that blast through the lava.
The remnants of a pseudocrater becomes a watering hole for the area sheep herds.
Basalt block fences are common on Icelandic farm lands.
This photo shows midges covering a part of a pseudocrater. The midges weren’t numerous when I was at Lake Myvatn, but they periodically emerge by the billions to cover the Lake Myvatn area. In fact, Lake Myvatn means “midge lake” in Icelandic. The midge populations are very closely tied to the Lake Myvatn fishery. Unfortunately, dredging in the lake during the 1960’s for a silicon mining operation has probably caused enough fluctuation in the midge populations to result in the collapse of the fishery. See the following publication for more information on this – High-amplitude fluctuations and alternative dynamical states of midges in Lake Myvatn.

Again – I’ll highly recommend that the best way to view Lake Myvatn’s pseudocraters is by tolting on an Icelandic horse!

Iceland Geology – Snorkeling the Silfra Fissure, Thingvellir National Park

I did a snorkel tour of the Silfra fissure with Dive.is while I was in Iceland a couple weeks ago. That is a very impressive way to view part of the mid-Atlantic ridge system! Here’s what Dive.is says about Silfra that makes it so unique:

Snorkeling the Silfra Fissure in Iceland.

“Silfra is a fissure between the North American and Eurasian tectonic plates in Thingvellir National Park. The rift was formed in 1789 by the earthquakes accompanying the divergent movement of the two tectonic plates . The diving and snorkeling site at Silfra is right where the two continents meet and drift apart about 2 cm per year. Silfra is the only place in the world where you can dive or snorkel directly in a crack between two tectonic plates. The earthquakes of 1789 opened up several fissures in the Thingvellir area, but the Silfra fissure cut into the underground spring filled with glacial meltwater from the nearby Langjökull glacier.”

My Silfra snorkel group starting out in the fissure with our guide Jake from Dive.is.

There are 6 people to a group for the snorkel tour, with each group accompanied by a guide from Dive.is. Jake was our guide and he was great! The tour is simply snorkeling through basalt and more basalt, but with the water clarity, the colors are beautiful. There is also one place where you can stretch across the fissure and basically touch both plates.

The start of the snorkel tour where the entrance platform can be seen in the background.
The stretch between plates…
This is where basalt really looks grand!
Near the end of the snorkel tour, the fissure opens into a shallow lagoonal area.
The colors in the sandy lagoon are just as spectacular as elsewhere in the fissure. The exit platform can be seen in the distance.
The end of the snorkel tour – ours was a great weather day, so even though the fissure water is cold (we all wear dry suits with long underwear and two pairs of wool socks), I could have snorkeled around the lagoon for a long time.

I also took video while I was snorkeling, so am inserting a clip from the first part of the snorkel tour at the end of this blog. The video clip includes the time when we all get geared up, have our gear checked, and then flipper-walk down the entrance ramp, into the water. We all have to do a flip over to our back once we’re in the water, just to make sure we can maneuver once we’re in the water. The clip continues on as we snorkel through the first several minutes of exploring the fissure. At the end of the snorkel tour, we hike back to where the Dive.is vans/equipment are. After taking off our gear – which getting off the dry suit is somewhat of a challenge – we have hot chocolate and cookies. Because the weather was so nice, it was a pleasurable experience to stand around and feast. But – we were told that in the wintertime the guides take the hot water that is suppose to be used for the hot chocolate and it pour down the snorkelers’ necks so the dry suits can be pulled off. Glad I opted for late May to do this!

Yellowstone To Southwest Montana Autumn Field Photo Snaps

Montana’s autumn is my favorite time of the year to do field work. Daytime temperatures are usually cool enough to encourage one to keep moving and the lighting is simply gorgeous. It is also one of the best times to visit areas in and around Yellowstone National Park (YNP) because most of the tourists have gone home. So no huge bear traffic jams or jostling for parking spots at the better known thermal spots in YNP and surrounding environs – it’s just a wonderfully introspective time for field forays. What follows are several photos that chronicle some of my fall wanderings in the greater Yellowstone area, both in terms of wildlife and geology.

Some of my favorite sightings in YNP are bison at any time of the year. But the autumn snows bring on the bison’s technique of using its head to clear snow away from any vegetative food source. The result of their snow-clearing activity is a snow-masked face.

Snow-caked face of a bison in YNP portends the winter food retrieval.

Snow-masked bison near Soda Butte Creek, YNP.

And where the snow hasn’t stacked up much, the YNP bison calmly graze and occasionally congregate on a ridge line to watch what remains of the YNP visitor traffic.

YNP bison contemplating passing vehicles.

Geological features in YNP take on new dimensions with the golden low and slanting light of autumn. I’ve spent much time re-photographing geologic features at all scales that seem to glow in this season’s light.

Tertiary sediments and Quaternary sediments/basalts of “The Narrows” cliff face adjacent to the Yellowstone River, northern YNP. Columnar basalt capped by auto-brecciated basalt makes a morel-like image for these geological units.

An early morning at -7 F on the Lamar River with steam fog resulting from the fall’s chilled air moving over water still warmed from summer.

A rodent trackway disappears into microterracettes of Palette Springs, Mammoth Hot Springs, YNP.

Microbial growth near the proximal part of Mound Springs, Mammoth Hot Springs, YNP.

The proximal end of Mound Springs abounds in various colored microbial life. It’s hard to stop photographing these features because they are so intriguing!

The lipped margin of Mound Spring’s pond facies, Mammoth Hot Springs, YNP.

The fall staging areas of sandhill cranes in southwestern Montana are mesmerizing. Staging areas are those locations where cranes annually congregate during late September into October, spend several days foraging through fields for food, and eventually continue on their migration southward from Montana to Colorado and the southwestern U.S.. The staging area that I usually go to is near Dillon, Montana, where hundreds of cranes can be viewed.

Sandhill crane interaction during their fall staging near Dillon, Montana.

Sandhill cranes doing a dance routine in the Dillon, Montana staging area.

As I said initially, it’s hard to surpass a Montana/YNP autumn!

Tertiary geology and paleontology of the central Gravelly Range – a project update

The 2017 field crew working at Lazyman Hill. The strata are late Eocene (probably 34-36 million years in age) tufa deposits.

It’s time for our yearly update talk on field work and data compilation for the Tertiary geology and paleontology of the central Gravelly Range project in southwestern Montana. The Madison Ranger District in Ennis, Montana (5 Forest Service Road) will be hosting my talk on Monday, April 2nd at 10am in the Madison Ranger District conference room. We have a project permit from the US Forest Service because our project area lies within the Madison Ranger District – and the USFS District people have been really helpful with our project logistics. Thus, this is the perfect way to let them know what we did this past field season and how the whole project is coming together. The Madison District just sent their public announcement for the talk:

Dr. Hanneman and Dr. Don Lofgren, PhD (Director, Raymond M. Alf Museum of Paleontology, Claremont, CA 91711) and their team have been executing a multiyear study in the Gravelly Range near Black Butte resulting in many interesting paleontological findings right here in our own back yard.  Please join Dr. Hanneman and the Madison Ranger District for an update on this project and what they hope to unearth this year!

It’s a very intriguing project on high-elevation, mainly Eocene-Oligocene Tertiary geology and paleontology (mostly vertebrate and floral). So – anyone with an interest in this and who is in the geographic area, is welcome at the talk!

Cuban Geology – An Updated Resource List

Vinales Valley in Cuba was designated a UNESCO World Heritage Site in 1999.

Within the last few weeks I’ve had several requests for available resources on Cuban geology. The requests, of course, have come from individuals outside of the U.S.A. Guess that they sense opportunities for working with and understanding Cuba’s geology that we are backing away from. In any case, I’ve sent the requests on to Manuel Iturralde-Vinet, the person who has worked and published an immense amount of information regarding Cuba’s geology. Manuel has now sent me back an updated list of resources and said:

You can advertise to all your friends and colleagues that a large
percentage of the geology, geography, paleontology, geophysics and
mining papers are free to be visited at
http://www.redciencia.cu/geobiblio/inicioEN.html

Other resources that are available include: http://www.redciencia.cu/cdorigen/arca/iturra.html

Field Trip Guides to Cuban Geology: 2001, IV Cuban Geological and Mining Congress: K-T Boundary of Western Cuba

— 2001, IV Cuban Geological and Mining Congress: Former Caribbean Plate Boundary, Camaguey, central Cuba

Compendio de Geología de Cuba y del Caribe. Segunda Edición 2012:
http://www.editorialcitmatel.cu/producto.php?producto=128

Videos de Viajes: http://www.youtube.com/user/IturraldeVinent2011#grid/user/A43949937C36E7BC

Videos de Geología y Naturaleza: http://www.youtube.com/user/IturraldeVinent2011#grid/user/DE8FDB5CE5960C19

Geological Society of America: The Geological Society’s (GSA) annual meeting in Denver, 2016, hosted a special session on the Geologic Evolution of Cuba. A link to session abstracts is: GSA Geologic Evolution of Cuba. The GSA Today October 2016 issue also highlighted Cuba Geology with the article “The geology of Cuba: A brief overview and synthesisauthored by Manuel Iturralde-Vinet and others.

Earth Magazine: Travels in Geology: Journeying Through Cuba’s Geology and Culture.

 

Irish Geo Travels – Northern Ireland

Traveling to Ireland has been something I’ve wanted to do. So, when the opportunity came up to go to Scotland, I couldn’t leave the general area without seeing at least some of both Northern Ireland and the Republic of Ireland. I only made it as far south as Dublin, but I guess on a positive side, that leaves many places that I need to visit on a future trip. I really wanted to go on a Cliffs of Moher Tour for example, as I’ve heard so many good things about them, but that’s one of the many things that will have to wait until next time unfortunately.

I flew from Glasgow into Dublin, rented a car, and first headed for Northern Ireland which is the subject of this blog. The causeway coastal route in Northern Ireland (from the North Channel coast eastward to the Irish Sea coastline) is a drive that I wanted to try. I ended up driving only about half of it – from Ballycastle east to Port Stewart because I spent so much time stopping to look at rocks and scenery.

The area that I drove through is a part of the Causeway coastline that cuts into the Antrim lava plateau. Beginning about 62 million years ago and continuing for several million years, extensive volcanic activity associated with the opening of the north Atlantic Ocean occurred here. In fact, igneous activity was so extensive in the nascent north Atlantic area, that the Antrim plateau basalts are only a small part of the North Atlantic Igneous Province, which is centered on Iceland. But – coming back more locally to the Antrim area, basaltic lava here intruded into Cretaceous marine strata, mainly chalk beds (which makes a striking visual contrast along the coastline). As noted on a Queen’s University Belfast website for the Giant’s Causeway:

The total area of these flows is now much reduced compared to their original extent, but they still constitute, at 3,800km2, Europe’s most extensive lava field. Traditionally the lavas of the Antrim Lava Group have been divided into three main phases of activity, separated by two extended periods of quiescence or limited, local activity.

The two areas that I spent most time at during my coastal causeway drive are the Carrick-a-rede Bridge and the Giant’s Causeway. These areas are developed within the Lower and Middle Basalts of the Antrim Lava Group and contain an Inter-basaltic Bed of reddish-weathered regolith and paleosols. A photo tour of the two areas are shown below –

Carrick-a-Rede Rope Bridge

A rope bridge connects the mainland with Carrick-a- Rede island. The first rope bridge was built in 1755 to facilitate fishing of Atlantic salmon. The salmon fishery has since died out, but the bridge is maintained as part of National Trust lands.

The Coastal Highway is cut into the Antrim Plateau where Paleocene basalt overlies Cretaceous chalk strata. The Lower and Middle Basalts of the Antrim Lava Group are in this area separated by a reddish-colored paleosol zone.

The hike to the Carrick-a-Rede Bridge goes over Paleocene basalt of the Antrim Lava Group.

A closer view of bridge – not too much wind when I visited, so it was a pleasant walk across the bridge.

Giant’s Causeway:

The Giant’s Causeway is a UNESCO World Heritage Site. As noted on its UNESCO website:

The Giant’s Causeway lies at the foot of the basalt cliffs along the sea coast on the edge of the Antrim plateau in Northern Ireland. It is made up of some 40,000 massive black basalt columns sticking out of the sea. The dramatic sight has inspired legends of giants striding over the sea to Scotland.

UNESCO World Heritage Site signage at the entrance to the Giant’s Causeway.

A Giant’s Causeway marker – This area was inscribed as a World Heritage site in 1986.

The paleosol zone of the lower Inter-Basaltic Bed exposed on the road to the Giant’s Causeway.

The onion skin basalt rocks at Windy Gap, on the road to the Giant’s Causeway basalt columns. These rocks have undergone much spheroidal weathering.

Causeway basalt columns…

More columns…

…and more columns. Halfway up the far slope is the reddish-colored lower inter-Basaltic bed that separates the Lower Basalt from the Middle Basalt of the Antrim Lava Group.

Siccar Point: A Day In The Field At Hutton’s Unconformity

Siccar Point – In June, 1778, James Hutton, John Playfair, and James Hall gazed on the rocks at Siccar Point and understood that an immense amount of geologic time was needed to produce the juxtaposition of underlying vertically-oriented (Silurian graywacke) bedded rocks with overlying near-horizontal (Devonian, Old Red Sandstone) rocks.

Siccar Point is unquestionably one of the most important geological sites in the understanding of geological time. It was here in 1778 that James Hutton, John Playfair, and James Hall contemplated the immensity of time needed to produce vertically oriented rocks overlain by gently-dipping rocks. The concept of geological time is so fundamental to the science of geology that I really wanted to explore the locality that gave rise to the idea of geological time. So I finally made the trip to Scotland and Siccar Point a couple weeks ago. Wow – what an amazing country! It was a fantastic trip, but for this blog, I’ll just post a few photos of Siccar Point – just enough, perhaps, to encourage geologic time enthusiasts to also make the trip.

Siccar Point is located on Scotland’s Berwickshire coast, about 40 km southeast of Edinburgh. It is not difficult to get there from Edinburgh for a beautiful day in any walking holidays in Scotland if you’re willing to drive a few back roads, and also drive on the left side of the road – which for me was somewhat of an initial challenge (going left on the roundabouts was mind boggling to begin with!). The best directions that I found for getting to Siccar Point are given by Angus Miller, who also runs field trips there. Angus’s directions to Siccar Point and his contact information are found at his Geowalks website.

The gate into the fields for the hike to Siccar Point.

The pull-off for the hike to Siccar Point is well marked by signage. All that one needs to do is walk through the gate and then follow the fence lines south to the Siccar Point locality. There is a small sign on the entrance gate that advises you to beware of the bull. We happened to meet up with a local person while we were hiking through the fields to Siccar Point and she told us that the land owner posted the sign mainly because he’s at war with the hordes of people that tromp through his fields to get to Siccar Point (in Scotland there is the “right to roam”, so one can hike across private property). She also assured us that at the time we were there, the cows were off in another field, so not to worry about the bull. We then just followed the hiking instructions on the sign at the gate entrance, and found that it’s an easy walk to Siccar Point.

The entrance sign to Siccar Point with hiking instructions.

The ruins of the St. Helen’s Chapel are found near the start of the hike to Siccar Point.

Much of the hike to Siccar Point is at field edges, near the sea cliffs.

The fence lines finally give way to the rock promontory that is Siccar Point.

Once one arrives at the rock promontory that is Siccar Point, it is an amazing view looking down the cliff face. The vertical beds of Silurian graywacke outcrop beautifully below Devonian Old Red Sandstone. The “Hutton Unconformity” here marks an approximately 80 million year hiatus. Again, there is also good signage present at the promontory for an explanation of the unconformity.

Siccar Point – the rock promontory that contains Hutton’s Unconformity.

Signage at Siccar Point well explains Hutton’s Unconformity.

A view to the south of Siccar Point where the underlying vertical beds of Silurian graywacke snake along the coast line, under the more gently dipping beds of the Devonian Old Red Sandstone.

 

 

 

 

 

A rope is attached to the fence at the promontory to help the climber down the cliff face. As it was a muddy and slick climb down to the North Sea, I was very glad to use the rope! Much thanks to whoever put the rope there!

Roping down the cliff face was a welcome way to get to the rocks below.

The rope climb back up Siccar Point – once again, I was very appreciative of the rope being there!

It was fun to investigate the unconformity at the sea’s edge. The base of the Old Red Sandstone contained lags from the graywacke, some of which are cobble size.

A closer view of Hutton’s Unconformity with the Old Red Sandstone atop the Silurian graywacke.

A layer of lag clasts at the base of the Old Red Sandstone. The vertically-oriented beds of the Silurian graywacke can be seen beneath the Old Red Sandstone.

A view back up the cliff face gives a good visual of the gently dipping Devonian Old Red Sandstone overlying the vertical beds of Silurian graywacke.

I know that we were very lucky to have good weather for our Siccar Point excursion, but I would have gone there whatever the weather. It is really one of the great geologic sites and well worth traveling part way around the world to see. For a drone view of Siccar Point, take a look at the video done by the British Geological Survey which is posted in an earlier Geopostings blog: Siccar Point from a drone’s view.

 

 

 

Central California Tectonics Field Trip

Deformation associated with the San Andreas Fault along Highway 14, near Palmdale, California. The strata in the roadcut are lower to middle Pliocene  gypsiferous, lacustrine rocks of the Anaverde Formation (a sag-pond deposit). Undeformed Pleistocene gravel unconformably overlies the Anaverde Formation.

 

I took part in a  central California tectonics field trip a few weeks ago that the Association for Women Geoscientists (AWG) sponsored. Tanya Atwater and Art Sylvester, professors emeriti at the University of California Santa Barbara, Department of Earth Sciences, led the field trip. During the field trip, we made numerous stops between Los Angeles and Hollister at areas where the San Andreas Fault bounds the North American/Pacific plates. Interspersed with fault-specific localities, we explored associated geology such as turbidites around Point Lobos, marine terraces in the Morro Bay area, and pillow/flow basalt at Port San Luis. The final stop on the field trip was an overlook on Santa Barbara geology at La Cumbre Peak with Tanya’s explanation on the tectonic evolution of the Transverse Ranges. If you are not familiar with the tectonic history of this general area, go to Tanya’s web site (http://emvc.geol.ucsb.edu/) and download her visualizations on global/regional tectonics. There are also visualization downloads on ice-age earth and sea level changes, so treat yourself to some very worthwhile earth science information by downloading these visualizations, too.

The following photos are from what I think are field trip highlights, including a brief caption regarding the geology shown in each photo. More information on many of the photo localities can be found in “Roadside Geology of Southern California“, 2016, by Art Sylvester and Elizabeth Gans.

Pallet Creek trench site, near Juniper Creek, consists of sag pond deposits that developed atop the San Andreas fault during the past 2000 years. These strata now underlie a terrace adjacent to Pallet Creek. In the late 1970’s, Kerry Sieh pioneered the idea of trenching strata along a fault to determine age constraints on fault movement at this locality.

On Tejon Pass, near Gorman, CA, it’s possible to place your feet on both the Pacific and the North American plates with little stretching effort. In this locality, the Pacific plate consists of quartz monzonite that is separated from the sandstone-silt strata of the North American plate by a zone of black-colored gouge developed along the San Andreas Fault.

Wallace Creek, a drainage from the Tremblor Range of the North American plate, takes a right-angle bend where it crosses the San Andreas Fault and enters the Pacific plate, The current offset is approximately 100 yards. Check out the aerial photo at http://epod.usra.edu/blog/2006/12/aerial-photo-of-wallace-creek-and-san-andreas-fault.html for a great view of the offset.

Cholame Creek near Parkfield, CA, delineates the trace of the San Andreas Fault. The plate boundary is well marked here and a similar sign is placed where one goes from the North American back to the Pacific plate.

The Parkfield Experiment is an earthquake research project focused on the San Andreas Fault. The USGS and the State of California are the primary agencies involved in this project. For more info on the project, go to https://earthquake.usgs.gov/research/parkfield/index.php.

Late Mesozoic Franciscan rocks along the Parkfield Grade are a chaotic assemblage of blocks of pillow basalt, chert, blue schist in a graywacke matrix. Note the scattered blocks of these rocks on the hillside and the blue schist block downslope in the foreground of this photo.

Pinnacles National Park contains remnants of the approximately 23 million-year old Neenach Volcanics. This volcanic area developed atop the San Andreas Fault system, and some Neenach rocks are now displaced northward on the west side of the San Andreas Fault system about 320 km.

In Old Town Hollister, CA, near Park Hill, a street curb is offset along the Calaveras fault.

Creep is occurring along the Calaveras fault in Old Town Hollister.

A building at the DeRose Vineyards near Hollister exhibits buckling due to movement along the San Andreas Fault.

A concrete drain ditch at DeRose Vineyards shows about 1 meter offset along the San Andreas Fault.

The San Juan Bautista mission west of Hollister is built adjacent to a straight hillside which is the San Andreas Fault scarp (located downslope from the white fence in the photo).

The Weston Beach area at Point Lobos, Monterrey Peninsula, has turbidite strata (the Paleocene Carmello Formation) that are contained within a submarine canyon that is cut into Silurian granitodiorite.

The Paleocene strata at Weston Beach are well know for their trace fossil assemblage. One of the more interesting, Hillichnus (shown in the central part of this photo), probably represents a feeding trace of a deposit-feeding bivalve.

The Tertiary volcanic rocks on Pinnacles National Park’s west side are also part of the Neenach volcanics originally located further south near Lancaster, CA. As noted above, the volcanics in Pinnacles National Park have been displaced about 320 km northwards along the San Andreas Fault system.

The Balconies Cave is a talus cave developed within the Tertiary volcanics on the west side of Pinnacles National Park.

Morro Rock is part of the Morro Rock-Islay Hill Complex. The complex is a series of 27-23 million-year old volcanic plugs that stretch for 29 km southeast of Morro Rock.

We stopped at the Montana de Oro State Park beach to see marine terraces (there are 6 terrace levels here). Unfortunately, because of the incoming marine layer, it was hard to see anything except an outcrop of the Miocene Monterrey Formation topped by Quaternary sediment.

Pillow basalt (23 million years in age) occurs at Port San Luis.

Pillow basalt is surrounded by shattered glass fragments at Port San Luis.

Pillow basalt is topped by ropy basalt flows at Port San Luis.

A view of Santa Barbara, CA, from La Cumbre Peak in the Transverse Ranges.  La Cumbre Peak tops out at 3,997 feet within the Santa Ynez Mountains north of Santa Barbara, California. The peak consists of  Eocene Matilija Sandstone. The existence of the Transverse Ranges is a topic that Tanya and her accompanying visualizations explain well. So once again – go to Tanya’s visualization web page and download her work on the Tranverse Ranges.

We are ready for the concert at La Cumbre Peak!! Great way to end a fantastic field trip.