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.


Hiking to Glacier National Park’s Grinnell Glacier

A few days ago I did the hike to Grinnell Glacier, one of the iconic glaciers in Glacier National Park. The glacier lies within the Swiftcurrent drainage area, in the northeastern part of the park. The hike, at least the way I did it, is about 11.6 miles round trip. It is possible to catch a boat ride at the Lake Josephine Boat Dock by the Many Glacier Hotel, which cuts the hike down to about 7.5 miles round trip. But – the first boat goes out at about 8.30 am, and as I didn’t want to wait around for it, I decided that adding on the extra miles for a fairly level stretch around Swiftcurrent Lake and Josephine Lake would be easy to do. It is an easy hike around the lakes and a very good warm-up for the rest of the climb to Grinnell Glacier. But –  be aware that this area is known for grizzly bear activity as I found out when I met up with a grizzly on the trail. Because I’m writing about this encounter,  it obviously ended OK, although I was glad I had bear spray readily available.

The glacier is named after George Bird Grinnell, who first explored this area during the summer of 1885. Because of bad weather, he did not actually get to the glacier during his 1885 travels. However, during the late fall of 1887, he was able to pack most of the way into the glacier by mules, and then hike the remaining distance by foot.  Although he certainly was not the first person to see the glacier, the glacier does bear his name, presumably given it by a Lieutenant John H. Beacom of the United States Army, 3rd Infantry, who accompanied him on the 1887 trip to the glacier.

It’s fun to see ripple marks in the Proterozoic rocks that outcrop along the Grinnell Glacier trail (Grinnell Lake is in the photo’s background).

Back to the hike – after about a mile from the junction of the Swiftcurrent Lake Trail with the trail coming from the North Shore of Lake Josephine boat dock, Grinnell Lake comes into view. A little further along the trail one can see Grinnell Falls dropping several hundred feet down from the headwall behind Grinnell Lake.

Grinnell Falls drops several hundred feet down from the headwall to Grinnell Lake. The Salamander Glacier can be seen in the photo’s upper right-hand corner; Gem Glacier is in the upper left-hand corner of the photo.

And – even at this distance, Salamander and Gem glaciers pop into view in the distant cirque. The hike continues along beautiful alpine meadows and even through one waterfall that cascades down the cliff adjacent to the trail. There is a rest area with pit toilets right before hiking the final switchbacks that traverse the terminal moraine to the Grinnell Glacier Overlook.

The final part of the Grinnell Glacier trail traverses the glacier’s terminal moraine.

Large boulder (Elrod’s Rock) in the Grinnell Glacier’s terminal moraine. Note the marmot atop the boulder for scale. The glacier’s terminus is now about a mile away from this boulder.

The three glaciers that once comprised the Grinnell Glacier occupy parts of a cirque developed along the area called the Garden Wall.

The cirque of the Grinnell, Salamander, and Gem glaciers.

Grinnell Glacier is still the largest of the three ice fields and covers about 152 acres. Unfortunately, this glacier is receding rapidly as the U.S.Geological Survey notes that from 1966 to 2005 it lost about 40% of its acreage. At about 5 acres, the hanging glacier called Gem Glacier, is the smallest named glacier in the park. It sits in the notch on the cliff face above the Grinnell Glacier. This glacier lost about 30 percent of its acreage from 1966 to 2005. The Salamander Glacier covers about 57 acres on a ledge off to the east side of the Grinnell Glacier. It apparently separated from the Grinnell Glacier sometime before 1929 and has undergone a 23% size reduction from 1966 to 2005.

For those interested in viewing photographs of the Grinnell Glacier from various times and viewpoints, the U.S. Geological Survey’s Repeat Photography Project has many archived photographs. This project is a documentation of glacial decline through photography and it is well worth perusing through their photo archives. Two of the earlier photographs are shown below – one from the original 1887 trek and a later view of the glacier from 1940 just to pique one’s interest.

1887 photograph of the Grinnell Glacier taken from footbridge (Lieutenant Beacon, Glacier NP. Public domain).

1887 photograph of the Grinnell Glacier taken from footbridge (Lieutenant Beacom, Glacier NP. Public domain).

Grinnell Glacier from trail 1900; Credit: F.E. Matthes, Glacier NP. Public domain.

Canadian Rockies – Alberta Badlands Geology Guidebook

The Canadian Rockies to Alberta Badlands geology guidebook is published by the Association for Women Geoscientists.

The Association for Women Geoscientists (AWG) published their first geology field trip guidebook in late 2016 and it is now available for sale to the general public. This guideboook is a collection of geology road logs, associated geological information, and local cultural history of areas within the Canadian Rockies and the Alberta Badlands. The following text is a brief summary of the guidebook:

“TECTONICS, CLIMATE CHANGE AND EVOLUTION – SOUTHERN CANADIAN CORDILLERA: Road Log and Accompanying Narratives From: Calgary – Lake Louise – Icefields – Field – Revelstoke – Fernie -Dinosaur Provincial Park – Calgary”, published by the Association for Women Geoscientists, 2016.

This field trip guidebook is written by Katherine J.E. Boggs and Debra L. Hanneman, and edited by Janet Wert Crampton and Stephanie Yager. It is the AWG’s first fully published field trip guidebook and is a field-tested guide from their two-week 2014 field trip through the Canadian Rockies and Alberta’s Badlands area.

The guidebook is a 209-page geology tour through many of the well-known parts of the Alberta Canadian Rockies, including the Front and Main Ranges of the Canadian Rockies and the Columbia Icefields. The Burgess Shale’s Walcott Quarry, the Okanagan Valley vineyards, and the Rocky Mountain Trench are trip highlights for geo-tours in British Columbia. The field trip guidebook ends with a geology tour of the Crowsnest Pass area on the British Columbia/Alberta border, and with field stops in Alberta’s Dinosaur Provincial Park and at the Royal Tyrrell Museum, Drumheller, Alberta.

The field guide is printed on double-sided 8.5″ x 11″ pages with the guide cover on 100 lb paper and the text on 80 lb paper. It has black wire-o binding and a clear acetate front and a black acetate backing for improved field durability. The guidebook’s cost is $55 USD (which includes shipping), and can be purchased at the AWG online store or by phoning the AWG main office at 303-412-6219.

Winter Trekking Through Yellowstone’s Thermal and Glacial Features

Cross country skiing in one of the glacial melt-water channels on the Blacktail Plateau.

Some winter days in Yellowstone National Park are so amazing with clear blue skies and sparkling snow that they just take your breathe away. Luckily enough, I just experienced several of these kinds of days which I packed full of cross country skiing, snowshoeing, and animal watching.

One of the groomed trails that held a good snow base until about early afternoon is the Blacktail Plateau Loop. The trail follows melt-water channels that are associated with “Retreat Lake”, which was formed by the Beartooth glacial ice mass blocking the lower end of the Grand Canyon of the Yellowstone during the Pleistocene.

Rounded cobbles and boulders left behind from melt-water flow sit on the volcanic bedrock in many areas along the trail. Ski tip in the lower right for scale.

Looking back to the northwest on the Blacktail Plateau ski trail. Notice the scoop-shape of the landscape which is the result of this area being part of a glacial melt-water channel.

Calcite Springs overlook is accessible during the winter via the Tower ski trail.

The Tower ski trail provides access to the Grand Canyon of the Yellowstone area. A favorite stop of mine is the Calcite Springs overlook where the thermal springs lie south of the overlook, on the west side of the Yellowstone River and Pliocene/Pleistocene sediment and basalt are on the Yellowstone River’s east side.


A groomed ski trail also accesses the Upper Terraces of Mammoth Hot Springs. However, after a few days of spring-like temperatures, the snow was so melted back that I just used my snowshoes to trek through the icy slush.  Some thermal features were still covered by snow and slush, but others appeared much more vibrant against the white snow/slush blanket.

One of the fissure ridges along the upper Terraces trail is called White Elephant Back Springs and Terrace.

Aphrodite Terraces lie a short way north of the White Elephant Back Springs:

My favorite thermal feature of the Upper Terraces is Orange Spring Mound. The spring is supported by a fissure ridge and is intermittently active. Because of its low water discharge and subsequent slow growth, it has built up a characteristic cone shape.

Orange Spring Mound of the Upper Terraces in Mammoth Hot Springs.

All in all, it was perfect wintertime fun trekking around in Yellowstone. Can’t wait to get back there when the bears come back out from hibernation!


Cusco, Peru – Markets, Ruins, and a Geologic Puzzle

During the 14th century, the Inca ruler Inca Pachacuteq (Tito Cusi Inca Yupanqui) transformed the central Andean area of present-day Cusco, Peru into a major urban center. The city became the capital of the Inca empire, containing religious and administrative areas that were surrounded by fertile agricultural expanses. In the 16th century, the Spanish conquered Cusco, building their Baroque churches and palaces atop the remnants of the Inca city. Today about half a million people live in Cusco. The city is now known for its amazing indigenous population and as a mecca for tourists that travel on to the Sacred Valley and Machu Picchu.

The Plaza de Armas in the UNESCO World Heritage site of Cusco. Our guide told me that there is a celebration in the square 360 days of each year!

The Plaza de Armas in the UNESCO World Heritage site of Cusco. Our guide told me that there is a celebration in the square 360 days of each year! I actually saw three different events there during my first afternoon in Cusco, so needless to say, the Plaza de Armas is a busy place.

Cusco Historic District

Cusco was declared a UNESCO World Heritage site in 1983 and the boundary for the site is mostly what is known as the Historic District (link here for a map of the UNESCO inscribed property). I did tour some of the buildings within the Historic District, my favorite being the Convent of Santo Domingo. The Spanish built this church on the remains of Qurikancha, a revered Incan temple for the Sun God Inti. The Inca stonework is the foundation for the cathedral and it is truly enthralling to see. Interestingly, numerous earthquakes have extensively damaged the cathedral, but the Inca stone walls still stand largely undamaged.

Convent of Santo Domingo built over the Qurikancha.

My guide, Ayul Acuna Cardenas, explaining the Incan stonework.

My guide, Ayul Acuna Cardenas, explaining the Incan stonework that was part of Qurikancha and now forms the foundation for the Convent of Santo Domingo.

The trapezoid-shaped windows that are characteristic of Inca architecture.

The trapezoidal windows that are characteristic of Inca architecture.









All kinds of goods are sold at the Vino Canchón market!


The chili selection at Vino Canchón is simply superb.


Vino Canchón’s fruit aisle is paradise for fruit lovers.


What a selection of cheese!


Many hotels get their fresh flowers daily from the Vino Canchón market.


The prepared food at Vino Canchón is a must to try!


The many varieties of Peruvian potatoes are overwhelming.


The Vino Canchón Market

The markets of Cusco – now they are an experience that can’t be missed. If you love food, Vino Canchón in the district of San Geronimo, is the place to go. This is the largest market in Cusco, supplying families as well as businesses with all kinds of produce, hardware, flowers, and many other items. It is also a market where the traditional Quechua language dominates the conversations. The Vino Canchón market is open daily and vendors are happy to talk with customers and the inquiring tourist.

Saqsaywaman and Its Geologic Puzzle

Saqsaywaman is the ruins of a fortified complex located at the northern edge of Cusco, on a hilltop that overlooks the city. As briefly summarized by Lake and others (2012):

“Most of the complex was demolished by Spanish settlers, who used the Incan stone to rebuild Cusco into a Spanish colonial town. What remains of the Saqsaywaman complex are large limestone blocks along with some shales, plasters and limonites which were too large for the Spanish settlers to easily remove. Some of these blocks are over 125 tonnes. Chroniclers state, that the construction ofSaqsaywaman was initiated by the ninth Inca, Pachacutec and was continued by his son Tupac Yupanqui Inca, between 1431 and 1508. The construction of Saqsaywaman is testament to the stonework engineering ability of its builder architects: Huallpa Rimachi Inca, the first and main Builder, followed by Maricachi Inca, Acahuanca Inca and Calla Cunchuy Inca. The remaining walls lean inward, which according to current theory allowed the Inca to create a more earthquake resistant structure, and are comprised of mortar-less joints so closely interlocked that even a single sheet of paper cannot fit between the blocks.”


Remnants of fortress walls at Saqsaywaman include large limestone slabs, some weighing over 125 tons.

A close view of the rock slabs showing indentations at slab bottoms which may have been used in a leverage process during fortress construction.

A close view of the rock slabs at Saqsaywaman showing indentations at slab bottoms which may have been used in a leverage process during fortress construction.







The Geologic Puzzle at Saqsaywaman

On the north side of the Saqsaywaman Archeological Park is a strange outcrop. The outcrop is andesite, but it is marked with north-east trending grooves. It is so deeply grooved in fact, that it’s known as “El Rodadero” – the roller coaster.


Close-up view of “El Rodadero” grooves in andesite.

In a quick scan of the geologic literature, it appears that ideas for groove formation have ranged from glacial grooves, to faulting, and to the andesite being plastic to partially molten as it was extruded and basically corrugated due to the overlying wallrock. The consensus on groove formation appears to be that of the viscous flow model, but here are links to the references I found, so decide for yourself:

  1. Spencer, J. , 1999,
  2. Spencer, J., 1999: Geology; April 1999; v. 27; no. 4; p. 327–330 (the complete article for the above abstract,
  3. Feininger, T, 1978: Geological Society of America Bulletin, v. 89, p. 494-503 (the initial article), and
  4. Schopf, J.M., 1979: Geological Society of America Bulletin, Part I, v. 90, p. 320, March 1979 (discussion on Feininger’s 1978 article).