An Incredible Spot in the Mojave Desert, the Hole in the Wall. You could see it for yourself this summer

Summer is coming soon. If you are casting about wondering what to do, how about the adventure of a lifetime? Our department is offering a dyad class, Geology 191/Anthropology 191, the Geology and Anthropology of the Colorado Plateau, and it is an incredible chance to check out some marvelous geology along our southwestern tier of states: California, Arizona, Colorado, Utah, and Nevada. I want to give you a bit of a preview of the kinds of places we will be visiting...

The Mojave National Preserve is one of our nation's newest parks (established in 1994). It was carved out from Bureau of Land Management lands in the eastern Mojave Desert, preserving one of the most awesome sand dune complexes in the country, the Kelso Dunes, a barren landscape of geologically recent volcanic cinder cones, one of the largest Joshua Tree forests in existence, and some of the highest mountain ranges in the Mojave Desert, with rocks as old as 1.7 billion years old, as ancient as those in the bottom of the Grand Canyon. The preserve also encompasses a California State Recreation Area, the Providence Mountains, and Mitchell Caverns, a unique limestone cave system. The caverns were closed during the recession, and then severely vandalized, but they have finally been reopened for visitation (see this Facebook page for updates).

One of the most interesting corners of the park is called Hole in the Wall, along with Banshee Canyon. We will be staying at the nearby campground our first night on the road on June 2. It is a wonderfully isolated spot, 25 miles off the main highway, and even farther from developments of any kind. It has some of the darkest night skies I've ever seen, and it is serenely quiet (except for crickets and coyote yowls).

The region is quite unlike other parts of the Mojave. Instead of deeply eroded mountain ranges and wide flat valleys, the area around Hole in the Wall is composed of mesas and plateaus that seem to share more in common with the Colorado Plateau province just to the east. But these mesas aren't like Arizona's either. They are composed not of sedimentary layers, but of volcanic tuff, rock derived from unimaginably huge volcanic explosions the likes of which modern humans have never experienced.

Twenty million years ago, the region was one of low relief, the result of tens of millions of years of erosion and relative stability. But conditions were changing as the crust was stretched and broken up into a series of tilted fault blocks. The release of pressure on the underlying mantle allowed partial melting to take place, and volcanic activity exploded across the region.

The first eruptions took place about 18.5 million years ago when the Peach Springs tuff coated the entire region from an eruption center near Oatman, Arizona. The eruption involved as much as 150 cubic miles (640 km³) of powdery white ash that was so hot that in many places it welded into solid rock as it landed.

Shortly afterward (in geologic terms anyway, as it was 700,000 years later), a second caldera developed. It was located even closer, in the adjacent Woods Mountains. The eruptive "crater", actually a collapse pit, was about 5-6 miles across, roughly similar in size to Crater Lake. Once again, all life was obliterated for hundreds of square miles as hot ash blanketed the landscape. The Wild Horse Mesa Tuff makes up most of the rock found at Hole in the Wall.

The strange holes that gave Hole in the Wall its name are called tafoni. Small differences in the degree of solidification or cementation cause depressions to form which end up staying wet longer, and the minerals decay into small fragments that can easily wash or blow away.

A short trail (1.5 miles) loops around Banshee Mountain and explores the best of the eroded tuff. Starting at the small visitor center, the trail drops through a rugged narrow canyon. There are some drop-offs, but rings have been attached to the canyon wall, making it a lot easier to climb up or down. Once past the narrows, the trail has a gentle gradient, and provides interesting views in all directions. There is a nice collection of petroglyphs on some of the boulders around the south end of the mountain.

If you want to visit this fascinating corner of the desert with us this June, please check out the previous post for details. We will be on the road for two weeks, and this will be only the first of many wonders that we will explore.

Dreams of Summer and Southwest Travels: Hole in the Wall, Mojave National Preserve

Christmas is over and suddenly the snow and blizzards aren't so fun any more. I find myself dreaming of warmer places and times, including a great journey we took last summer across the southwest with my students. Since my current travels are over until February, I'm going to travel through the archives to check out some marvelous geology along our southwestern tier of states: Arizona, New Mexico, Colorado, Utah, and Nevada. But really, no place is more southwestern than California, where we will start this journey.

The Mojave National Preserve is one of our nation's newest parks (established in 1994). It was carved out from Bureau of Land Management lands in the eastern Mojave Desert, preserving one of the most awesome sand dune complexes in the country, the Kelso Dunes, a barren landscape of geologically recent volcanic cinder cones, one of the largest Joshua Tree forests in existence, and some of the highest mountain ranges in the Mojave Desert, with rocks as old as 1.7 billion years old, as ancient as those in the bottom of the Grand Canyon. The preserve also encompasses a California State Recreation Area, the Providence Mountains, and Mitchell Caverns, a unique limestone cave system. The caverns were closed during the recession, and then severely vandalized, but there are hopes that they will reopen in 2016 (see this Facebook page for updates).

One of the most interesting corners of the park is called Hole in the Wall, along with Banshee Canyon. We stayed at the nearby campground our first night on the road. It is a wonderfully isolated spot, 25 miles off the main highway, and even farther from developments of any kind. It has some of the darkest night skies I've ever seen, and it is serenely quiet (except for crickets and coyote yowls).

The region is quite unlike other parts of the Mojave. Instead of deeply eroded mountain ranges and wide flat valleys, the area around Hole in the Wall is composed of mesas and plateaus that seem to share more in common with the Colorado Plateau province just to the east. But these mesas aren't like Arizona's either. They are composed not of sedimentary layers, but of volcanic tuff, rock derived from unimaginably huge volcanic explosions the likes of which modern humans have never experienced.

Twenty million years ago, the region was one of low relief, the result of tens of millions of years of erosion and relative stability. But conditions were changing as the crust was stretched and broken up into a series of tilted fault blocks. The release of pressure on the underlying mantle allowed partial melting to take place, and volcanic activity exploded across the region.

The first eruptions took place about 18.5 million years ago when the Peach Springs tuff coated the entire region from an eruption center near Oatman, Arizona. The eruption involved as much as 150 cubic miles (640 km³) of powdery white ash that was so hot that in many places it welded into solid rock as it landed.

Shortly afterward (in geologic terms, anyway, as it was 700,000 years later), a second caldera developed. It was located even closer, in the adjacent Woods Mountains. The eruptive "crater", actually a collapse pit, was about 5-6 miles across, roughly similar in size to Crater Lake. Once again, all life was obliterated for hundreds of square miles as hot ash blanketed the landscape. The Wild Horse Mesa Tuff makes up most of the rock found at Hole in the Wall.

The strange holes that gave Hole in the Wall its name are called tafoni. Small differences in the degree of solidification or cementation cause depressions to form which end up staying wet longer, and the minerals decay into small fragments that can easily wash or blow away.

A short trail (1.5 miles) loops around Banshee Mountain and explores the best of the eroded tuff. Starting at the small visitor center, the trail drops through a rugged narrow canyon. There are some drop-offs, but rings have been attached to the canyon wall, making it a lot easier to climb up or down. Once past the narrows, the trail has a gentle gradient, and provides interesting views in all directions. There is a nice collection of petroglyphs on some of the boulders around the south end of the mountain.

If you want to visit this fascinating corner of the desert, you'll have to search it out. It's not a quick roadside stop, but is instead a place to take a bit of time to explore. The time is well worth it!

Picture of Peach Springs Tuff (with Big Bird Bonus)

The Internet connection at our hinterlands location is slow and undependable, so tonight is just a picture of the Peach Springs Tuff, an 18.5 million year old rhyolite tuff that covered a vast area between Peach Springs Arizona and the Mojave Desert near Barstow. It is nicely exposed along the old Route 66 in Kingman Arizona, which was one of our stops today. There also seems to be a large fledgling bird sitting on the rock and partly blocking the view, but I found it interesting. I am assuming it is a Red Tailed Hawk fledgling. Is there anyone who can confirm or correct?

Dangit! There's a Jackass Tailgating Me! A Day in Oatman Arizona

How many puns can a man take (or tell)? Today we were on the road again, and true to my resolution, I went someplace new. We were traveling into Arizona, and I knew that there was a stretch of the original Route 66 that passed through the small gold mining town of Oatman. I didn't read up on the site ahead of time, so the presence of their famous 'wild' burros was a bit of surprise. The town is a tourist destination these days, with daily old west gunfights, the Clark Gable/Carole Lombard honeymoon suite at the Oatman Hotel (and a ghost), and lots of curio shops, but the town has an interesting geologic history as well. The burros are the feral descendants of burros who escaped from or were abandoned by the early miners.

There is a jackass in this picture. Oh, and also a burro on the right.

The rocks here at the southern end of the Black Mountains of Arizona are late Cenozoic volcanic tuffs and lava flows which have been eroded into scenic pinnacles and spires. The source of the very extensive Peach Springs Tuff was a caldera in the immediate vicinity of Oatman. The eruption took place 18-19 million years ago, and covered a region extending from Barstow, California to Peach Springs in Arizona. Tens of cubic miles of volcanic ash were blasted into the atmosphere during the catastrophic eruption. Gold and silver have been mined in the region since 1863, with the main production at Oatman between 1915 and 1942. Gold production in the region amounted to about 2.2 million ounces. The Gold Road Mine above town looked to be active when we passed by.

Oatman had a slightly more sinister reputation, at least to the thousands of Dust Bowl refugees who passed this way in the 1930s. The town is located in some rugged mountainous terrain, and Route 66 originally passed through town. The road is steep and winding, and must have been nerve-wracking to the folks driving ancient cars with brakes and transmissions of dubious quality.

Beyond Oatman lay the Colorado River and the vast Mojave Desert of California. Although it is easily traversed today on modern freeways, in the 1930s a summertime passage could be terrifying and dangerous. My grandparents made the journey in the early 1940s, driving at night to avoid the worst of the heat. The town was bypassed in 1953 when a less rugged stretch of highway connected Kingman with the town of Needles in California on the Colorado River.

But on this day, the mountains were beautiful, the road a pleasant drive, and the burros were just being themselves: complete jackasses...