Spring Break 2016 – Joshua Tree National Park

Field Trip Rationale

On August 25th 2016, the National Park Service will celebrate its 100th birthday and there is no better way to honor this momentous event than to spend time learning about one of these beautiful natural landscapes. Because of its rich geologic past, Joshua Tree National Park, CA was selected as the 2016 Spring Break geo-destination. Spanning over 790,000 acres, the park hosts approximately ~2 Ga of Earth’s history, which is recorded in the various rock units exposed throughout the region. This history includes ~1.9 Ga Proterozoic gneisses, marbles, and quartzites, Mesozoic monzogranites, diorites, and peraluminous granites, alluvial fans of the Tertiary and Pleistocene,and more (geologically) recent volcanism, faulting, and tectonic uplift. This location therefore provided a fantastic setting in which students could apply classroom-based knowledge to world-class field outcrops.

Haleighs photo
The granites, Joshua Trees and desert environment of Joshua Tree National Park, CA (photo credit: Haleigh Richards)

Fieldtrip Leaders

Dr. Kenneth (Kenny) Brown – brownkl3@miamioh.edu

Dr. Claire McLeod – mcleodcl@miamioh.edu

Claire getting very excited about granites.
Kenny pointing out towards 2 billion years of geological history recorded in Joshua Tree National Park.

Joshua Tree National Park: Geologic Snapshot

The old metamorphic basement in Joshua Tree National Park provides a window into the deep roots of long-eroded mountain belts which once stood tall on an ancient landmass known as Rodinia. Associated with these lithologies are strongly foliated gneisses which outcrop on the Lost Horse Mine trail (Day 3) and along the Ryan Mountain trail (Day 3), two of our planned field destinations this week.

The mountain ranges these rocks once underlain stretched from the Baltic region of modern day northern Europe, across the United States out to California and perhaps beyond. One school of thought is that the old gneisses of the Joshua Tree area are related to the gneisses of modern-day Australia. Another idea is that the gnesisses are linked to the Trans-Antarctic Mountains near the South Pole. This would suggest that once upon a time, California and Australia ± Antarctica were neighbors! Today they define the Trans (continental)-Rodinian Mountains. As the supercontinent of Rodinia broke up and the proto-Pacific Ocean formed ~800 Ma, the Joshua Tree region would have been characterized by a marine continental shelf with bedrock submerged in shallow seas. This geological environment would remain in place for ~550 Myrs.

During the Paleozoic (545-251 million years ago), life began to thrive on Earth but little evidence of this time period is preserved in the rocks in and around Joshua Tree. At c. 300 Ma, the continental landmasses formed the supercontinent Pangaea, with Joshua Tree on its northwestern coast.  As Pangaea broke up, rifting north to south, a proto-Atlantic Ocean formed. The North American continent moved west and faulting and folding began to accommodate the heavy sediment loads on the lithosphere and rising shelf edges. This ended ~500 Myrs of low-lying, submerged continental shelf-like environments in the region of Joshua Tree.

To the west of the region, the oceanic plate began to subduct beneath the North American continent, potentially as far as ~650 km depth into the Earth’s mantle. One idea is that this descending plate sank as far east as Colorado and Texas, with some pieces breaking off and sinking to the core-mantle boundary, about 3000 km depth! Mountain building was once again active, forming the Nevadan Mountains which are parental to the modern-day California mountain ranges. The ancient Rodinian lithologies did not get forgotten as the bedrock underwent a second stage of metamorphism associated with this younger phase of mountain-building. Associated with this subduction regime is the production of granite, for which the Joshua Tree National Park is world-renowned for. The granites of Joshua Tree formed incrementally over millions of years forming plutons, large separate crystalline masses (named after Pluto, Roman God of the underworld). Particular outcrops of note, and certain field destinations for this trip, include the Palms Monzogranite of Hidden Valley (Day 3),  the Megacrystic Potassium Feldspar Granite at Rattlesnake Canyon and Fortynine Palms Oasis (Day 6) and the White Tank Monzogranite at the base of Malapai Hill (Day 4).

Around 75 Ma the angle of subduction beneath western California began to shallow, leading to a shutdown of the established magmatic systems, hence the youngest granites in the National Park are ~75 Myrs old. Forty million years later subduction steepened again and magmatism resturned briefly to this part of the western USA, although the reason for this is not well understood. At ~25  Ma, the tectonic plate configuration changed from subduction to strike-slip faulting. This is characterized today by the San Andreas Fault which will be observed from Keys View (Day 3) during this trip and is arguably the most famous fault in the world (and recent focus of the latest movie from Dwayne “The Rock” Johnson).

The final stages of magmatic activity, as this compressional regime switched to one of shearing, is represented by lava flows (mesas and bluffs) (Day 2) along the edges of the Pinto Basin in Joshua Tree National Park.  Minor volcanism intermittently occurred following shutdown of the collisional regime due to crustal stretching and thinning along faults. The release of pressure provided pathways for mantle-derived melts to ascend towards the surface through the older granites and basement gneisses. Evidence of this late-stage volcanism at Joshua Tree will be seen on this trip at Amboy Crater (Day 2), Malapai Hill (Day 4) and at Lower Covington Flats (Day 5) where basalts and mantle xenoliths (peridotites) can be found. The age of this volcanism across the park has been to constrained to as young as 100,000 to potentially 15 Ma!

In short, there is plenty to see and do and experience out in California!

MARCH 19th – MARCH 25th 

DAY 1 – March 19th: Cincinnati, OH – Las Vegas, NV – Needles, CA

This year’s Department of Geology and Environmental Earth Science Spring Break trip (#RockSpringBreak) is heading to Joshua Tree National Park – California here we come!!

Heading west – cruising at 35,000ft over the snow-capped mountains of Colorado.

Stop 1 – The Las Vegas Strip

After landing in Las Vegas, NV in the late afternoon and learning that many of the students had never seen the unique, eclectic culture and theme park-like atmosphere of the city of Las Vegas, we took a quick drive down the strip before heading out into the desert and onto Needles, CA, our destination for the night. Highlights of the whistle-stop tour down the strip included the rollercoaster associated with the New York, New York hotel, the Paris hotel and the fountains of the Bellagio.

Vegas 1
The New York, New York hotel on the Las Vegas Strip. Several of the towers are designed to replicate the famous Empire State and Chrysler Buildings. A 150ft tall replica statue of the Statue of Liberty stands at front of the hotel.
Vegas 2
The Paris Las Vegas hotel complete with a 541ft replica of the Eiffel Tower.

Leaving the bustling city behind, the drive out to Needles, CA took us out and across the quiet and deserted desert of Nevada. We passed through the small and isolated town of Searchlight before stopping on the outskirts of Needles, CA for dinner at a diner called Juicys (named after the founders lost dog) where we all met up for some much needed food and had a good time! (in joke).

Stop 2 – Juicy’s

“Juicy’s Famous River Cafe” in Needles, CA provided dinner on Day 1 of our trip. According to Yelp, this was the #1 place to eat in Needles.

Geo joke of the day – How fast does a fault move? A mylonite (A mile a night)

Fact of the Day – The word “pluton” is derived from the Roman God Pluto, God of the Underworld.

Quote of the Day – Austen reflecting on the #1 place to eat in Needles, CA “We all met up at Juicy’s and had a good time.”


DAY 2, March 20th – Needles, CA – Joshua Tree (National Park), CA

Our day started in Needles, CA, specifically in the Denny’s next our Motel 6 in Needles, CA – ranked #15 of places to eat in Needles according to Yelp.

Our stay in Needles was short but sweet. A quiet little, quirky Californian town ideally located for our first nights sleep.

The sun was up and it was getting warm by the time we hit the highway heading towards Amboy Crater to the north of Joshua Tree National Park. Our route took us along the famous Route 66 and we stopped ~45 minutes east of Amboy to overlook the landscape we were heading in to, give our legs a much needed stretch and take in some of the Route 66 art work.

Stop 1 – Overlook to Amboy Crater on Route 66

Route 66 is one of the most famous roads in America and runs for 2448 miles from Chicago, Illinois to Santa Monica, California. 314 of those miles are in California. It is also known as the Will Rogers Highway, the Main Street of America or the Mother Road.

rt 66 art
Heading west to Amboy Crater and Joshua Tree National Park on historic Route 66.
Overlook point to the west along historic Route 66 towards Amboy Crater and the ghost town of Amboy. Amboy Crater is a 264ft tall volcanic center. The magmatic activity associated with it represents some of the youngest magmatic activity in this region of the western USA.

Stop 2 – Amboy Crater

Through the town of Amboy, across the railroad tracks on Route 66 and past the exit to Joshua Tree National Park is a road to a small parking lot and information boards for visitors detailing information about the local geology, ecology and biology at Amboy Crater. Amboy Crater was designated a National Natural Landmark in 1973.

Hiking out to Amboy Crater. Amboy Crater is located in the Barstow-Bristol trough, a major structural depression trending W-NW and is broadly located at the boundary between the Mojave and Sonoran tectonic blocks. According to the sign, the most recently active volcanism was only 10,000 years ago.

More information regarding Amboy Crater from the Bureau of Land Management is available here:


For more information specifically on the volcanism at Amboy:


The hike up to the summit of Amboy Crater provided opportunities for students to observe textures associated with minor volcanism and minerals associated with these types of rocks; basalts. The lava flows are predominantly pahoehoe and if looked at closely, small green olivine (Mg,Fe)2SiO4 crystals could be seen shining in the bright California sunshine. Also clearly visible was the basalts vesiculated texture; abundant vesicles characterizing potential paleoflow directions indicating that when the magma erupted, and as the lava cooled, volatile components exsolved (likely H2O, CO2, perhaps H2SO4 as well).

The hike up to the top of the crater was a 3-mile round trip and offered wonderful 360o views of the surrounding landscape. We all made it up and even managed big smiles for the first of many a group photo!

Hiking up to the top of the crater walls and beautiful 360 degree views!
We made it to the top – beautiful veiws overlooking the Mojave Desert! #GoRedhawks #MiamiOH

Stop 3 -Roy’s Motel and Cafe on historic Route 66

We drove back east on historic Route 66 to the town of Amboy and a late-lunch stop at Roy’s Motel and Cafe. It also serves as a gas station and auto-repair shop. It was originally opened in 1938 by its founder Roy Crowl at a time when Route 66 was the primary east-west highway across the USA. In 1972 California’s I-40 was opened and essentially isolated Roy’s from business. The town of Amboy was sold for $425,000 in May 2005 to preservation patron (Albert Okura) who worked to restore Roy’s to its original Route 66 glory.  The coffee shop and gas station re-opened in 2008 and provided us with some much-needed water, food and rest after our hike in the intense desert heat. Fun facts: both Harrison Ford and Anthony Hopkins have visited this historic Route 66 stop, the town of Amboy was used in Enrique Iglesias’ hit single “Hero” and Brad Pitts 1993 movie Kalifornia was filmed here.

Amboy 1
Inside Roy’s Cafe, a throwback to historic times on Route 66.
Amboy 2
High gas prices at Roy’s gas station due to the high cost of delivery to the remote location.
Miami University, OH leaving their mark on Route 66 at Roy’s Cafe, Amboy, CA.

Leaving a little piece of Route 66 history behind we drove south on Amboy Road towards the town of Twentynine Palms. On either side of the road ~3 miles south of Amboy lay Bristol Dry Lake which contains ~60 million tons of salt in reserve. The surface is characterized by clay, gypsum and sand. Beneath the surface is the mineral halite, (sodium chloride – NaCl) which is actively mined today. Continuing south we stopped on a dirt road (left-hand side) leading to the Needles Field Station. Taking care not to park on the gas pipe clearly marked, we ventured out to explore our first granite of the trip.

Stop 3 – Megacrystic Granite

This particular geo-stop is broadly located in western part of the Sheephole Valley Wilderness area which hosts the Sheephole Mountains. To the west of Amboy Road lie the Bullion Mountains which are visible across the road from this location.

Parking up our sturdy field vehicles in front of some very feldspar-rich granites! (a white Chevrolet Suburban and a dark-grey Chrysler mini-van)

On the hillside in front of the vehicles (above) granite outcropped and it wasn’t hard to quickly realize this granite was easily recognizable by its large potassium feldspars.

Large “megacrystic” potassium feldspars characterize the granite outcropping near the Needles Field Station. Overall the granite is fairly weathered – finding a fresh surface between the K-spar crystals was difficult! Biotite and Quartz also present.
Kenny on the hunt for megacrystic feldspars with graduate student Alex Opsitnick (left) and sophmore student Haleigh Richards (right).

Continuing south on (north) Amboy Road and then right on route 62, we headed east towards Twentynine Palms through Wonder Valley, characterized by numerous abandoned houses and cabins.

For more information on the abandoned homesteads:


We stopped at the Joshua Tree National Park visitor center (Oasis Visitor Center) in the town of Twentynine Palms (turn left off route 62 down Utah Trail). This provided a nice opportunity to pick up some maps of the park for the coming week, learn a little park history and be tourists for a little while with the purchase of many a postcard, magnet, t-shirt and sticker. Feeling hungry we stopped for Mexican food in the town Twentynine Palms at Edchadas where we were sat as a large group in an old bank vault and devoured ~25 baskets of chips (accompanied by a slightly smaller amount of salsa). Following dinner we stocked up on food a local grocery store for breakfasts and lunches days before continuing east to the town of Joshua Tree and our accommodation for the next 4 nights.

Stop 4 – our Airbnb house for the week!

For our stay in the Joshua Tree area we had rented a house through Airbnb and a local journalist and artist named Hilary Sloane (more about that on Day 6). In short, her house was wonderful! This provided the ideal base for our group, spacious kitchen and living room space, large garden with extensive patio, telescope and hottub and a very homely atmosphere.

The main living room (left) and main entrance hallway (right) of our house for the duration of our stay in Joshua Tree National Park.
The front (left) and back (right) entrances to our Airbnb house located a few miles outside of the entrance to Joshua Tree National Park.
sunset Day 1
Sunset over Joshua Tree and the end to our first day out west. Photo Credit: Steven Janson.

Geo joke of the day – What do cows make when there is an earthquake? Milkshakes!

Fact of the Day – Crystals in the field can look like the wooden mineral blocks from mineralogy. Mineralogy wasn’t a lie after all. #SymmetryIsReal

Quote of the Day – Kenny’s field rules – “No rocks, no ice-cream!”


DAY 3, March 21st – Joshua Tree National Park: overview geology, basement rocks and granite


Stop 1 – Keys View

This morning brought with it our first venture into Joshua Tree National Park. Our first stop was Keys View located on the Little San Bernardino Mountains located 20-minute drive from Park Boulevard. From here you can see beautiful panoramic views over Coachella Valley through the valley runs the San Andreas Fault which stretches 700 miles north of San Francisco to the Gulf of California. Across the valley Palm Springs can also be seen, which hosts over 100 golf courses and behind which lies the 10,800ft San Jacinto Peak. To the northwest Los Angeles could be seen over which dense, grey smog had settled in and the snow-covered peak of the 11,485ft San Gorgonio Mountain, the highest peak in southern California could be observed to the west.

day 3
View to the west from Keys View Point. The Santa Rosa Mountains can be seen across the valley with the highest point at San Jacinto Peak (10,831ft, left). This peak is more than twice the height of the mountains in Joshua Tree National Park. The town of Palm Springs is nestled at the foot of San Jacinto and hosts nearly 100 golf courses. The Gorgonio Pass funnels the smog-heavy air from southern California into the Coachella Valley. San Gorgonio, the highest peak in southern California (11,485ft) is not shown in the above images but could be seen to the northwest.

The outcrops to the left of the view point provided an opportunity for us to see some granites up close and personal for the first time on this trip. The granites belong to the Big Horn sheeted complex and quartz, plagioclase feldspar, biotite (mica) and amphibole were easily identified. Looking closer, garnet and sphene/titanite (a calcium titanium silicate, CaTiSiO5) were also spied through the aid of a hand lens and a keen eye.

Undergraduate student Steven Janson inspecting garnets in the granites of the Big Horn Sheeted Complex.
field day 3
Garnet present in the peraluminous granites of the Big Horn Sheeted Complex (left). Students exploring the granite outcrop and enjoying the view over the Coachella Valley (right).

Stop 2 – Lost Horse Mine Trail

Following our stop at Keys View and our introduction to some of the granites Joshua Tree National Park had to offer, we drove further east into the park to the Lost Horse Mine Trail.  The Lost Horse Mine is near the summit of Lost Horse Mountain and is located between the southern end of Hidden Valley and Queen Valley. Along the start of the trail Proterozoic ortho- and para-gneisses, amphibolites and hornblende gabbros were exposed. The hike out to the Lost Horse Mine was ~2 miles and allowed us to see some of the deserts other unique features, mainly cacti!


Hiking the 2 mile trail out to Lost Horse Mine.
The desert can be beautiful but deadly! Claret Cup Cactus in bloom (left) and getting up close and personal with a Jumping Cholla cactus (right) – jumping because its spikes will detach easily when brushed up against!
Kenny vs. Jumping Cholla cactus. Cactus wins.

Geology of the Lost Horse Mine

From Trent (see link below): Sampson and Tucker (1945) report the ore body is one or more quartz veins that occur in micaceous quartzite and granite. However, the host rock is clearly granitic quartz biotite gneiss; the Proterozoic Lost Horse pelitic granofels of the Pinto Gneiss according to Powell (1980). Coleman, et al, (2003) map it as orthogneiss and with U-Pb ages of ~1715 and ~1700 Ma. The gold-bearing quartz vein in the mine varies in width from six inches to five feet (Sampson and Tucker, 1945).

The Lost Horse Mine is one of the best-preserved mills under National Park protection. Mining plays an important part in the history of the Joshua National Park area. In the park itself there are 747 mine openings.

For more information on the mining history of Joshua Tree National Park:


lost horse mine
Lunchtime at the Lost Horse Mine. The mine produced more than 10,000 ounces of gold and 16,000 ounces of silver (worth ~$5 million today) between 1894 and 1931.

The Story of Lost Horse Mine (the story below is taken from the National Park Service, the link is included below).


As long-time resident William F. Keys, told the story, Johnny Lang and his father drove their herd of cattle into the Lost Horse Valley in 1890, when there was “nothing but cattle and Indians.” Johnny told Keys that they had moved west after his brother and six other cowboys were gunned down in New Mexico. One night, while camped in the Lost Horse Valley, the Langs’s horses disappeared. Next morning Johnny tracked them to the McHaney brothers’ camp near today’s Keys Ranch. According to local legend, the McHaney Gang were cattle rustlers. Keys said they told Johnny his horses weren’t there and to leave the area.

Keys goes on to say that Johnny met up with a man named “Dutch” Frank who told of also being threatened by the McHaneys. Frank said that he had discovered a rich claim but was afraid to develop it. Johnny and his father bought the rights to the mine for $1000 and called it Lost Horse. To reduce the chances of being killed by the McHaney Gang or having his claim jumped, Johnny took on three partners. After filing their claim, they set up a two-stamp mill and began processing gold.

A wealthy rancher from Montana, J.D. Ryan, bought out Johnny’s partners in 1895. The next year he found a steam-powered, ten-stamp mill somewhere near the Colorado River and had it dismantled and hauled to the mine site. To provide steam for the mill, Ryan ran a two-inch pipeline 3.5 miles, from wells at his ranch to an earth and stone reservoir near the mill. Steam engines fueled by trees from nearby mountains were used to push the water up the 750 foot elevation gain where it was boiled to power the stamp mill. Heating the water at both the ranch and the mill required a lot of wood, and the results of the timbering can be seen today in the sparsely vegetated hillsides at both sites.

Getting to the Gold

The booming of the ten 850-pound stamps could be heard echoing across the valley 24 hours a day as the ore was crushed. Water added to the crushed rock made a slurry, which washed over copper plates covered with a thin film of mercury. The gold particles clung to the mercury and the debris washed away.

The amalgam of mercury and gold was smelted to separate the two metals. The mercury could be reused and the gold was formed into bricks. These bricks were carried to Banning every week, concealed in a 16-horse freight wagon. The 130-mile trip to deliver the gold and return with supplies took five days.

As the story goes, the day shift was producing an amalgam the size of a baseball while the night shift, supervised by Lang, recovered a mere golf ball. Ryan hired a detective to investigate and discovered that when Johnny removed the amalgam from the copper plates, he kept half for himself. Ryan gave Lang a choice: sell out or go to jail. Lang sold, then moved into a nearby canyon where he continued to prospect.

The Lost Horse Mine continued producing until 1905, when the miners hit a fault line and forever lost the ore-bearing vein. The mine was leased to others or left dormant until 1931, when rising gold prices prompted the processing of 600 tons of tailings (unprocessed chunks of leftover ore) with cyanide, producing a few hundred ounces of gold.

During one of the mine’s dormant phases, Lang returned and set up residence in the cookhouse. According to Keys, Lang had hidden his stolen amalgam at the mill site and, unable to get to it before Ryan ran him off, had returned to retrieve his stash. Lang sold what Keys called “pure gold bullion” on several occasions during this time. In the winter of 1925, sickly and unable to walk out for help, Johnny Lang died of exposure along Keys View Road. Two months later, Keys found his body and buried him across from the access road to the mine.

Stop 3 – Ryan Mountain

Following our hike to the Lost Horse Mine we drove to the start of the Ryan Mountain trail.


Ryan Mountain was named after two brothers, Thomas and Jep who once had a homestead at the base of the mountain. The trail leads to a summit at 5457ft after a 1070ft gain in elevation. The early part of the trail is dominated on both sides by exfoliated granite domes (Mesozoic). Surrounding these and easily visible on the steeper parts of the trail are the basement into which these granites intruded; gneisses and schists.

Exfoliated granite domes dominate the start of the Ryan Mountain trail.
Ryan Mount
Weathered Mesozoic granite domes at the start of the trail (left). Intensely folded gneiss outcrops on the trail on route to the summit (right).

As the trail ascends and moves west the Wonderland of Rocks, a suite of jumbled rock formations which define the “classic Joshua Tree landscape” can be seen to the northwest. Further west, the Little San Bernardino Mountains can be seen rising above the park. The upper section of the trail leads to views to the north and east over the Pinto Basin.

Views out over the Pinto Basin from the upper section of the trail, Joshua Trees and Jumping Cholla continue to line the sides of the trail.
We made it to the top – 5457ft! The best place in the park to look over the “heart of the park”.

Geo joke of the day – What do you call a periodic table with Gold missing? Au revoir!

Fact of the Day – Most things in the desert are trying to kill you.

Quote of the Day – Steven on the production at Lost Horse mine “25 million dollars came out of THAT little hole?!”


DAY 4, March 22nd – Joshua Tree National Park: recent magmatism, the ecotone and petroglyphs

The Geology Tour Road runs for 18 miles through Queens Valley and into Pleasant Valley in the center of the National Park and was our destination for the morning. 4WD vehicles were recommended but in the name of geology and adventure (and lack of 4WD), we made a swift exit from Park Boulevard and ventured on!

The Geology Tour Road Map –


Numbered markers line the road of the Geology Tour Road, 16 stops in total. A guide to each location can be found on the following links –



Stop 1 – Malapai Hill (Stop 7 on the Geology Tour Road)

Malapai Hill represents some of the most recent magmatic activity in this region. It rises ~400m from the valley floor and is characterized by two peaks. This relatively young magmatism intrudes the older White Tank monzogranite (~151Ma) which outcrops nearer the road and at the foot of the hill itself.

Stopping our 4WD-absent vehicles at Stop #7 on the Geology Tour Road (left). Hiking up to Malapai Hill through outcrops of the White Tank Monzogranite, cacti and Joshua Trees (right).
Beavertail Cactus (Opuntia Basilaris) and its characteristic pink/purple flower adding a dash of vibrant color to the Mojave Desert throughout Joshua Tree National Park (left). Its green stems are flat and wide, like the tail of a beaver. A Joshua Tree (Yucca Brevifolia) is broadly confined to the Mojave Desert at elevations between 1300ft and 5900ft (right).

The word “Malapai” is derived from the spanish word “Malpaís” which refers to a rough and barren landscape comprised of largely uneroded lava fields: “bad terrain”.  The two peaks are comprised of alkaline olivine basalt. Olivine crystals were clearly visible in many of the talus blocks dominating the hill scarps. Also present are mantle xenoliths although many of them are heavily weathered. These mantle xenoliths likely represent the composition of the underlying depleted mantle beneath the western United States.

Lherzolitic mantle xenolith in Malapai Hill basalts – 1.5cm in length. Chromium diopside was also observed (left). At the top of Malapai Hill enjoying the view out towards Pleasant Valley to the south and east (right).
Potential scenarios for the formation of Malapai Hill (credit: National Park Service Geology Tour Road Guide) – was Malapai Hill intrusive or extrusive?
Notebooks on top of Malapai Hill record the comings and goings of previous visitors to the summit.
Names and dates of Malapai Hill visitors throughout the years. Miami University Geology Spring Break 2016 made their mark! (right). On closer inspection  of the other notebook, a familiar name appeared – 5 years ago Kenny was at this very spot! (left).

From recent work of Muller et al. (2014, see link below) the basalts at Malapai Hill have been dated at 15.93 Ma implying that they represent some of the oldest volcanic centers in the Mojave region. It is inferred that their emplacement is likely associated with extension and shear related to the San Andreas Fault system.


Stop 2 – The Geology Tour Road Loop

Following our descent of Malapai Hill we returned to the car and continued south on the Geology Tour Road. The one-way loop provided views north back towards Malapai Hill (see below) and across Pleasant Valley. In the basement of the valley the Pinto Gneiss outcropped into which the White Tank monzogranite and Malapai Hill magmas would have intruded many millions of years later.

tour road
Assessing our vehicles likelihood of survival down the rocky tour loop (left) – we went for it! (and even made friends with some Toyota drivers and passengers along the way). Looking north to Malapai Hill and across Pleasant Valley (right).

Stop 3 – Crossing the Ecotone

Driving further into the park heading east along Park Boulevard past Skull Rock and Jumbo Rocks there was a striking change in vegetation. This change marked us crossing the ecotone between the Mojave Desert and the Sonoran Desert. The Joshua Trees started to diminish and the landscape became characterized by the Whipple Cholla cactus.

An ecotone simply marks a transition zone where one plant community changes into another plant community. This is typically attributed to a change in environment e.g. elevation.

Left: Joshua Trees characterize the landscape of the Mojave Desert. Heading east and crossing the ecotone the landscape becomes dominated by smaller vegetation, primarily the Whipple Cholla cactus (right).

Stop 4 – Barker Dam and Petroglyphs

Taking Park Boulevard back west we stopped at Barker Dam. Not only did the trail here lead out to the Dam (also known as Big Horn Dam) but it also offered us the opportunity to experience a part of the parks history we had not yet encountered; ancient petroglyphs associated with the Native American communities who once lived in the park. Round trip, the trail was ~1.3 miles and offered more opportunities to see extensive outcrops of the parks Mesozoic granites and many Joshua Trees.

The trail out to Barker Dam:


Barker Dam located between the Wonderland of Rocks and Queen Valley. In 2013 the Dam was closed to the public due to vandalism but has since re-opened.
barker dam
Big Horn (or Barker) Dam was originally constructed in the 1900 by early cattlemen. In 1949, William F. Keys raised it. The inscription in the rocks reads: Big Horn Damn Built by Willis Keys, W. F. Keyes, Phyllis M. Keys, 1949-1950 (left). Present day water level (right).

Following the trail around to the west the path leads through a beautiful area of granite boulders and Joshua Trees before passing several rock faces on the left on which several Native American petroglyphs and pictographs are visible.

Walking through the granites and Joshua Trees west of Barker Dam to the Native American petroglyphs and pictographs of the Cahuilla Indians.

The petroglyph and pictograph location on the Barker Dam trail loop is authentic and visible to the naked eye. However many of the pictographs are visible thanks to the Disney Company. In the 1950’s film studio filmed scenes from “Chico, the Misunderstood Coyote”. They painted over the original designs to make them visually stand out more on film. Petroglyphs are designs that are pecked or have been scratched into rock. Pictographs are designs that have been painted onto the rocks.

Petroglyphs and Pictographs on the Barker Dam trail.

Geo joke of the dayWhy are geophysicists such hipsters? Because they are SO underground!

Fact of the Day – It is against National Park rules to climb on outcrops with Native American petroglyphs on them.

Quote of the Day – Haleigh after falling down Malapai Hill: “I’m not on a snake so what does it matter?!”


DAY 5, March 23rd – Joshua Tree National Park: crustal basement rocks, Samuelson’s Rocks, recent magmatism, tilted lower crustal section

Our third full day in the National Park focused on outcrops to the west which comprised the basement to which the later Mesozoic granites intruded into and assimilated and the granites themselves.

Stop 1 – Schists and Amphibolites

Entering the park at the Joshua Tree entrance we drove for a few miles down Park Boulevard and parked the vans just off the road to the left in a small parking area, near  a trail head that headed to a stack of rocks ~100ft away. Crossing the road we walked the floor of Lost Horse Valley towards a few hummocks, a ~30 minute walk from the road with Quail Mountain in the background to our left and the Lower Covington Flats on the other side of that (our destination that afternoon).

day 5
Hiking out over the Lost Horse Valley floor to our first outcrop of the day. Over the mountains in the background lies the Covington Flats (afternoon stop) and out to the right (after a small hike) Samuelson’s rocks, our second stop of the day (left). One of many pretty Joshua Trees on the valley floor (right).
From the classroom to the field: graduate student Alex Opsitnick (left) and undergraduate student Erin Graves (right) inspecting the dark, shiny, biotite-rich crustal basement rocks.

This outcrop provided us with our first up, close and personal look into what the Mesozoic granites of Joshua Tree National Park likely intruded into and interacted with during their emplacement. On Day 3 we saw amphibolites and the folded ortho- and para-gneisses along the Lost Horse Mine Trail. The rocks here were notably different; micaceous (biotite-rich) with small (<1mm) garnets. Also present was sillimanite, a high-temperature, medium pressure aluminosilicate phase (Al2SiO5). Known as index minerals, the presence or absence of the different alumnosilicate phases (kyanite and andalusite being the others) can be used to infer pressure and temperature conditions of formation. In this outcrop, 2-5mm long, <1mm wide elongate sillimanite crystals could be seen with the naked eye (and the help of a hand lens, see photo below).

From L-R: Kenny, Rob Skourmal (graduate student), Austen Rubenstein (undergraduate student), Erin Lary (undergraduate student), Alex Opsitnick (graduate student) – identifying sillimanite in the field.
Kenny continuing the hunt for good examples of sillimanite in the biotite-garnet mica schists (left). Hiking around the small hill and dropping down into the valley again we came across a small water pumping station. After a few pumps on the lever, fresh groundwater flowed out along a tube and into a drinking trough – fresh and delicious! (right).

Stop 2 – John Samuelson’s Rocks

Heading north/northwest along the valley floor and through a maze of Joshua Trees and cacti we walked to John Samuelson’s rocks, a set of granite boulders that rose prominently above the surrounding area. These granites were heavily veined (see below, left) and provided clear evidence of interaction with, and assimilation of, surrounding country, crustal basement lithologies (see below, right). Also present were small (<2-3cm) mafic enclaves which provided evidence of magma mingling during granite emplacement.

Strongly veined (quartz) granite at Samuelson’s Rocks (left). Evidence of crustal basement interaction and assimilation. Quartz veins are also present to the right and left of the crustal xenolith (right).

These particular outcrops of granites are also named Samuelson’s Rocks after John Samuelson.

John Samuelson was an area ranch hand and miner in the 1920’s at Key’s Ranch. He was a citizen of Sweden and Samuelson claimed to have spent a majority of his life at sea. In 1927, John Samuelson decided to homestead his own piece of property in Lost Horse Valley. He built his humble shack on top of a small hill, and mined his gold claims. In his spare time Samuelson carved political slogans, or musings, on the boulders near his home.

“Mother time. Neither wealth law’s nor army’s can stop the human mind from creating new or emprove up on the present day religion and government. Water is saft onley hard in the chemicall’s but with time the ocean can griend the hardest granit into a powdered sane. So with time will the human race griend out it’s own destiny’s regardless of the opposition or party in power”
“Religion is a code of moralls for us to live by no more. Hell is here on this earth no other plase. Most of it we make. Our selfe. As to haven find it in a lifetime nothing proven after death by preast or scientist?”
Left: The Rock. Of faiht. And truht. Nature. Is. God. The. Key. To. Life. Is. Contact. Evolution. Is. The mother and father of mankind. Without them. We. Be. Nothing. John Samuelson. 1927. Right: Judge Ben Lindsey A. Man that understands humanety and big anough to. Live. It. Study nature obey the laws of it you can’t go wrong it payes compund enterest for life and not one penny envested?
On the left: Wake up you tax and bond slaves. A politician is a bird that gets in on the tax payors poket book for a fat rake of and his free keep’s. He lead’s you by the noose with one hand with the other he digs in your pocket. A freind of the banker and big business why.?. On the right: Are you the fellow Mr. Mellon that grabed all our dough. Ain’t you better up and tell us. Where in hell did it go.

Stop 3 – Lower Covington Flats (recent magmatism and tilted crustal section)

Following our lunch stop at Samuelson’s rocks we headed out of the National Park, drove west along route 62 before turning south on La Catenta Road towards the Lower Convington Flat area. At the end of the dirt road is a small parking area.

Exploring the northwestern tip of Joshua Tree National Park at the Lower Covington Flats area.

We hiked into the valley to the left of the parking lot and followed a small trail/dried up river bed to the northeast. On either side of the valley walls tilted, visibly layered and deformed crustal blocks were easily seen. These Late Cretaceous outcrops represented the deepest part of the tilted crustal section exposed here at Joshua Tree National Park and were once ~20km under the Earth’s surface (determined from Aluminum in hornblende).

Hiking out to the tilted lower crustal section along a dried-up river bed (left). Tilted crustal blocks visible in the valley walls (right). Continuing down the valley to the northeast would have brought us (eventually) back to Samuelson’s rocks.
Deformed layers and cross cutting relationships in the lower crustal section, evidence that intrusion of silica rich fluids occurred whilst host lithology was not solid (left). Folding and layering in well defined melanosomes and leucosomes, clear field evidence for partial melting in the lower crustal section (right).

Stop 4 – Eureka Peak

For our last stop of the day we continued along the dusty, dirt-road up to Eureka Peak ~4 miles from the Covingtoin Flats area. Eureka Peak is the 4th highest point in Joshua Tree National Park at 5516ft and offered beautiful views across the Coachella Valley and Morongo Basin to the west and northwest.

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Sun setting over the Little San Bernardino Mountains.
Ending the day on a high, literally. Beautiful views across the Coachella Valley, Morongo Basin and the San Andreas Fault system.

Geo joke of the day – Are you bored of seeing granite yet? Of Quartz not!

Fact of the Day – Geophysicists obsess over the amount of force required to knock over Cap Rock.

Quote of the Day – Kenny despairing at dinner “You can guys can make all these observations about the chips but you can’t make a single observation about a rock!”


DAY 6, March 24thJoshua Tree National Park, CA – Laughlin, NV

Today marked our last day in the Park. Before our day in the field began we spent time being interviewed by local artist and journalist Hilary Sloane. Hilary owned the house we had rented for our stay in Joshua Tree and she was interested in finding out what we had seen during our stay in the area, why we had visited the region, what our favorite places in the park had been and why we were all studying the Earth Sciences. Being interviewed was an exciting (and nerve-wracking!) experience but it gave us a good opportunity to reflect on what had been a wonderful time in the park and think about what we would take away from the trip.

Joshua Tree interview
Local journalist and artist Hilary Sloane talking to us about our trip to Joshua Tree National Park and our interests within the field of Earth Science.
Group photo with house owner and local journalist and artist Hilary Sloane (center). From L-R: Erin, Savannah, Theresa, Max, Erin, Steven, Austen, Hilary, Grant, Rob, Kenny, Beth, Haleigh, Alex.

Driving east along route 62 (Twentynine Palms Highway) we exited south on Canyon Road and headed for the trail start to Fortynine Palms Oasis.


Stop 1 – Fortynine Palms Oasis

At the start and along the majority of the trail out to the oasis are outcrops of the Triassic potassium feldspar Twentynine Palms quartz monzogranite characterized by potassium feldspar, plagioclase feldspar, amphibole and quartz. The potassium feldspars were easily seen as loose crystals along the trail (see below).

Graduate student Alex Opsitnick and undergraduate student Haleigh Richards examining potassium feldspar megacrysts on route to Fortynine Palms Oasis.
The day was getting hot as we started the ~1.5 mile hike towards Fortynine Palms Oasis (left). On route Kenny attempted to teach the local wildlife a lesson or two in granite petrology (right).
Top left: Trail out to Fortynine Palm Oasis crosses the Queen Mountain Monzogranite and the Twentynine Palms Quartz Monzogranite. Top right and bottom left: megacrystic K-feldspars in the Twentynine Palms Quartz Monzogranite. Bottom right: View of Fortynine Palms Oasis with the Cretaceous, garnet-two mica granite outcropping in the vicinity of the Palm Trees (notable lack of megacrystic feldspars, garnet easily seen by the naked eye).
The last stop of our Spring Break 2016 trip in Joshua Tree National Park! Plenty of rocks and smiles at the Fortynine Palms Oasis, it was beautiful!
Kenny and Claire excited to be out in the field looking at rocks. They were more impressed by the megacrystic feldspars than the oasis at Fortynine Palms.
Beautiful views to the north from Fortynine Palms Oasis (3 mile hike round-trip).
Tracing the water in the oasis at Fortynine Palms. Photo credit: Max Leveridge.
We kicked some dust up driving around Joshua Tree National Park!

Following our last stop in the National Park, our destination was Laughlin, NV nestled close to the intersection of California, Nevada and Arizona. Heading out east on route 62 we then turned north through the Sheephole Valley Wilderness area before passing through Amboy (Day 1) and back onto Route 66, eventually arriving into Laughlin, NV.

Geo joke of the day – The more you try to be gneiss, the more you get taken for granite!

Fact of the Day – Geology IS awesome.

Quote of the Day – “Fried ice-cream in the field, how could it get any better?!”


DAY 7, March 25th – Laughlin – Las Vegas, NV

Leaving Laughlin early enough to stop at Hoover Dam before heading to the airport we drove west on route 163, north on route 95 and east on route 93 up to Boulder City and the “modern civil engineering wonder of the United States” one of seven as selected by the American Society of Civil Engineers in 1955; the Hoover Dam.

Stop 1 – Hoover Dam, Nevada

Construction of the Hoover Dam started in 1931 and 5 years later the Dam opened. The dam is located in the Black Canyon of the Colorado River on the border between Nevada and Arizona. The dam is 726ft tall and was the largest dam in the world at the time of its construction.
The body of water behind the dam is known as Lake Mead, the worlds largest reservoir. With the building of the Hoover Dam the development Las Vegas, Los Angeles and Phoenix was spurned as its 17 turbines have the potential to generate enough electricity to power 1.3 million homes.
hoover dam 2
The Mike O’Callaghan-Pat Tillman memorial bridge over the Colorado River from Nevada to Arizona. During its construction it was known as the Hoover Dam Bypass Project (left). During construction of the Hoover Dam, 96 men lost their lives. A memorial to them stands on the Nevada side of the dam (right).

Stop 2 – Las Vegas airport – home to Ohio we go!

vegas sign
Our flight out of Las Vegas took us across the stunning Grand Canyon of Arizona at sunset – the perfect “adios” to Spring Break 2016!

See you for Spring Break 2017!


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