Monday, October 29, 2012

Views of the Bottom of a Lake

Cathedral Gorge State Park campground (photo source).
On a hot Nevada afternoon back in September, I happily collapsed in the shade of a campsite at Cathedral Gorge State Park in Meadow Valley just north of Panaca.  After a refreshing siesta, I set out on a tour of the bottom of a lake.
View of a lake bottom, through "geologically enlightened eyes."
Only 5 Ma (million years ago), just a moment geologically-speaking, this was a much cooler wetter place.  Meadow Valley was a closed drainage basin with a lake in the bottom.  Water flowed in but not out, and creeks and runoff carried in gravel, sand, silt, clay, gunk and dead animals.  Some 1400 feet of sediments accumulated, enough to provide spectacular scenery for modern-day visitors.

It’s tempting to view landscapes as static.  There’s an earthquake every now and then, or a landslide here and there, but generally we see little change over the course of our lives.  But at the scale of the Earth’s life, its surface is anything but static.  The huge plates that make up the crust are constantly jostling, colliding, shoving, diving, splitting and even stretching.  It was expansion of the Great Basin that created Meadow Valley, along with the other valleys and mountains of the Basin and Range Province.  At some point, maybe as recently as the late Pleistocene (only 100,000 years ago or so), the region was tilted, “spilling” the lake down Meadow Valley Wash.  Erosion went to work on the exposed lake bed, carving out badlands and sending sediments down the wash, on the move once again.
Badlands -- "heavily eroded, uncultivable land with little vegetation" (Oxford American Dictionaries).  Yup, these look to be badlands alright, can't grow much here!
Not all lacustrine (lake) deposits are eroded into such striking and curious forms, so there must be something special about these sediments.  They started out as volcanic ash, produced in huge explosive eruptions during the incredible volcanic mayhem of the Great Basin in mid-Tertiary time, roughly 40 to 20 Ma.  This was a hell of a place, quite literally.  Flows of red-hot ash raced across the landscape, incinerating everything along the way.  Wind-borne ash clouds obscured all sunlight.  Incandescent flows glowing in constant darkness must have been terrifying!   Ash in the flows was so hot that it fused to form welded tuff or ignimbrite (from Latin for fire-shower).  The remains of the catastrophic eruptions  -- extensive outcrops of welded tuff -- are common in the Great Basin.

So much magma was removed from these violent volcanoes that they collapsed and formed calderas -- monstrous depressions miles across.  Just a short distance south of Cathedral Gorge is the huge Caliente Caldera complex, about 20 miles across north to south, and 50 miles east to west.  It produced vast amounts of ash and welded tuff over its 9-million-year lifetime, including some that ended up in the Cathedral Gorge badlands.
Major mid-Tertiary calderas; based on DeCourten 2003, Taylor and Switzer 2001.
The old eruptions still cause problems -- welded tuff south of Caliente tends to fall on the highway.
Caliente may be a sleepy little town now, but it was a happening place 20 million years ago!
Rock is ephemeral, of course, and weathering and erosion went to work reducing the Caliente welded tuffs to silt and clay.  Some of this accumulated in the bottom of the lake in Meadow Valley, eventually producing 1400 feet of rock, much of it poorly-cemented, easily-eroded, clay-rich and sticky when wet.  This is the Panaca Formation, famous for its abundant small mammal fossils, and named for the town of Panaca, famous for its annual dutch oven cook-offs.

Not all Panaca strata are soft.  There are thin beds of resistant limestone that form "caps" protecting softer rocks from erosion.  It's because of these caps that the Panaca is sculpted into fanciful castles and hoodoos, and tall narrow “caves”.
Panaca Formation, with thin layers of freshwater limestone on top of softer strata.
Narrow gullies with tall, nearly-vertical walls (two visible on left) are called "caves".  The big hoodoo on the right is the most famous one in the park, note book cover below.
Trails of water rivulets -- marks of the sculptor's hand.
Sculptures are short-lived.  Remnants of old scenery form low piles below today’s badlands.
Just think ... this crumbling rock once was searing volcanic ash that raced across the landscape burning everything in its path, and then was welded into tuff, weathered and eroded, deposited in a lake, exposed when the lake was emptied, and sculpted into badlands.  What a great story!  It's so wonderful that we can decipher something of the geological history.  For me, it makes these beautiful landscapes even more fascinating.
“... in preparing to behold beauty in landscapes, there is something very special about seeing the land through geologically enlightened eyes.”  Frank DeCourten, The Broken Land - Adventures in Great Basin Geology

Miller Point Overlook, with views of Cathedral Gorge and the Great Basin beyond.
Cathedral Gorge State Park is located in southern Nevada, just off US Highway 93 about 10 miles south of Pioche, 25 miles north of Caliente, and just a few miles north of Panaca.  It is roughly 175 miles from Las Vegas via I-15 and US 93.  The campground features showers and shady sites, and there is a small system of hiking trails -- the longest loop is 4 miles.  A scenic and fairly easy trail goes from the picnic area up a drainage through beautiful badlands to the Miller Point Overlook.
Stairs make the final ascent through soft Panaca “rocks” possible.
It was so nice to hike in the cool of the evening ...
... and watch the sun set, with an appropriately fiery display!

Sources and Additional Information

Most of the information in this post is from two trusty Great-Basin-roadtrip companions:

DeCourten, F.L.  2003.  The Broken Land; adventures in Great Basin geology.  Salt Lake City: University of Utah Press.

Orndorff, R.L., Wieder, R.W. and Filkorn, H.F.  2001.  Geology underfoot in central Nevada.  Missoula, MT:  Mountain Press Publishing Co.

Looking for Detachment posted about Cathedral Gorge State Park here and here.

and from Academia:

Lindsay, E. et al.  2002.  Recognition of the Hemphillian/Blancan boundary in Nevada.  J. Vert. Paleont.  22:429-442.

Pederson, J. L. et al.  2000.  Neogene through Quaternary hillslope records, basin sedimentation, and landscape evolution of southeastern Nevada.  GSA Field Guide 2 pp 117-134.

Scott, R.B. et al.  1996.  Synchronous Oligocene and Miocene extension and magmatism in the vicinity of caldera complexes in southeastern Nevada.  Denver:  CO Geol. Surv. Open-File Rep. 96-4, Field Trip No. 7.  

Taylor, W.J. and Switzer, D.D.  2001.  Temporal changes in fault strike (to 90º) and extension directions during multiple episodes of extension: An example from eastern Nevada.  GSA Bulletin 113 pp 743–759.


  1. This place is new to me - I would love to visit it. It's beautiful. At the same time, for all that it is less terrifying than it may have been in pre-history, I think I would find it pretty frightening now. I don't think I could cope with being there for very long.

    1. Interesting, Lucy ... reminded me of my reactions to the harshly beautiful landscapes in Utah and Nevada. They're wonderful to visit but I always think "I could never live here, too bizarre!"

  2. That was a beautiful description. I love reading about the back-story of an area, based on the geology.