Burners at incipient plate boundary in western Nevada. Are they waving California goodbye? (original unknown)

Many times I've crossed Nevada in the company of Frank DeCourten and Norma Biggar (hereafter called D & B). Actually I've never met either one, but I know their Roadside Geology of Nevada well. That's where I learned of the state's traumatic history—torn apart, reassembled, buried in ash and welded rock, and now being torn apart again. These stories can be hard to grasp, but I've read and reread the lengthy introduction enough to be awestruck by landscapes that many travelers find dull.

Sturdily bound, with high quality paper—my copy has survived lots of use.

Maps, diagrams and photos are abundant!

In the eight years since D & B published their book, I've often parked off the highway at their suggestion to study and photograph a geologic feature. I think of this as geohopping to geostops, rather than my usual geotripping to geosights (and later blogging about it). Now it's time to give the geostops their due.

One of my favorite stretches of highway between Laramie, Wyoming (home) and the California Central Coast (home of relatives) is US 6 across Nevada. Traffic is light, towns are few, and the geology truly is dramatic!

Geo highlights along US Highway 6, May 2025.

For example, about thirty million years ago, widespread cataclysmic destruction associated with the Great Ignimbrite Flareup (GIF) created Hell right here on Earth. Supervolcanoes erupted repeatedly across today's Nevada depositing ash thousands of feet deep, much of it welded into rock by the searing heat ("ignimbrite" means "fire cloud rock"). Trying to recreate that terrifying Flareup in my mind is one of the joys of driving across Nevada.

But it's impossible to properly imagine the GIF, in part because "no volcanic eruptions ever witnessed by humans come close to rivaling these prehistoric paroxysms." And the geologic record suggests it may be one of the largest ever. Consider this: in Nevada at least 230 supervolcanoes ejected an estimated 17,000 cubic miles of lava! Here's another way to think about it: at least 30 of these eruptions each equaled 600 Mt. St. Helens eruptions!

Blue Jay Maintenance Station on left, remnants of cataclysmic destruction behind.

Eye of the Ichthyosaur

My visit to the volcanoes of eastern California last May was far too short, but there was nothing I could do. Life called. So after hiking up Panum volcano I raced east past Mono Lake, crossed into Nevada in the Bodie Hills, stopped briefly for gas and groceries in Hawthorne, and raced on. My destination was Berlin in the Shoshone Mountains.

This would be my third attempt. The first was canceled by the covid pandemic. Then the park shut down while pandemic stimulus funds were used for road improvements (still unpaved and washes out occasionally, so check before going). But this year I made it, just in time to set up camp before dark.

Looking west from Berlin across Ione Valley to the Paradise Range beyond, a fine example of the basin-and-range topography that covers much of Nevada.

Berlin is one of Nevada's many abandoned gold-mining towns. It was at its peak at the turn of the century (19th–20th), with a population of about 250 miners and their support staff: blacksmiths, woodcutters, charbonniers, a doctor, a nurse, and a prostitute. Yet by 1911 everyone was gone, a typical boom–bust story. But Berlin didn't disappear entirely. Some buildings remained intact long enough for history buffs to drum up protection.

Berlin Mill in 1910.

Two stamp batteries center bottom, for crushing ore plus water and mercury.

Several decades later Berlin experienced a revival of sorts, thanks to the many curiously-shaped stones in a draw nearby (miners supposedly used them as dinner plates!). In 1928 paleontologist Siemon Mueller of Stanford University examined them, and determined that they were fossilized bones of large marine reptiles—ichthyosaurs. But he left the fossils in place due the remoteness of the site.

Tiktaalik, what were you thinking?! Zina Deretsky, NSF.

In the midst of planning a tour of Paleozoic time in the Great Basin—a way to escape from this confusing disturbing world—I learned that thousands of people share my feelings. Amazing! What made the Paleozoic so alluring? It was a fish, specifically a charismatic fish that ventured onto land 375 million years ago. Tiktaalik (tic-TAH-lick) and its brethren are the progenitors of amphibians, reptiles, birds, and mammals. Yes, it was wandering fish—our ancestor—that got us into this mess!

Urban legend has it that Tiktaalik lived in a late Devonian paradise. The climate was mild. Stream banks, swamps, and other places where water met land were lush with delicious nutritious plants. Life was good. There was no reason to go back to the sea, at least not yet.

But life wasn't perfect. These early tretrapods most likely were stumblers rather than walkers. It probably took them all day to find enough food, and they could not escape predators. But as one paleontologist pointed out, Tiktaalik and its brethren were not burdened with self-awareness. “Everyone is, like, only barely conscious of the idea that they’re alive.” (Ben Otoo, U. Chicago grad student)

Now the Earth is occupied by creatures greatly burdened with self-awareness. Memers rage that Tiktaalik should have stayed in the ocean, thereby saving us all. Maybe those folks should return to the Paleozoic sea themselves. That's what I plan to do.

In the "desert ranges which lie to the west as far as longitude 117° 30' there is no considerable mountain body without its exposure of Palaeozoic strata" (geologist Clarence King, 1878).

Today's Great Basin is rich in remnants of the Paleozoic sea that covered much of today's Nevada and Utah. That sea was born about 700 million years ago, when the supercontinent Rodinea was breaking up. The former west half of Nevada drifted away, leaving the eastern part and adjacent Utah underwater. This was a passive continental margin, on a single tectonic plate. There was no tectonic jostling, only geological serenity (DeCourten 2003). Tens of thousands of feet of sediment accumulated on the sinking ocean floor.

In the 150 years since, much has changed. The single range is now two: the East Humboldt Range to the north and the Ruby Mountains to the south, separated by today's Secret Pass (formerly Sacred Pass). A pass in the southern Rubies that used to honor explorer John Frémont is now Harrison Pass. It was here that the geologists discovered a dramatic change. To the south were thick beds of sediments deposited in a Paleozoic sea. To the north was a huge mass of seriously deformed rock.

King took it upon himself to study the area north of Frémont's Pass. He assigned the deformed rocks to the Archaean, which at that time included all Earth history before the Cambrian. King concluded these rocks had been an island in a Paleozoic sea. This was a reasonable hypothesis, not at all out of line with current thinking. But that too has changed.

Ruby Mountains and vicinity; points of interest in red (after Snoke et al. 1997).

A year earlier, 25-year-old Clarence King—young, bright, and ambitious—had persuaded Congress to fund a Geological Exploration of the Fortieth Parallel, which he would lead. His assignment was broadly defined—"a geological and topographical exploration of the territory between the Rocky Mountains and the Sierra Nevada ...".

King must have been ecstatic. This was a region poorly known geologically and ripe for discovery. He and his crew spent seven seasons in the field. The result was a large atlas of topographic and geologic maps, and seven reports, published from 1877 to 1880.

Volume II, Descriptive Geology, was the first (Hague & Emmons 1877). Arnold Hague wrote the section about the East Humboldt Range. He began with the area south of Frémont's (Harrison) Pass, in today's southern Ruby Mountains. Here were very thick beds of Paleozoic rocks, with limestone conformably overlying quartzite. "The quartzites appear a little calcareous and the limestones somewhat siliceous, but the transition is made by a rapid passage from one to the other."

North of Frémont's Pass "a change takes place in the rock ...", noted Hague laconically. In fact it was a dramatic change. The thick beds of Paleozoic sediments were replaced with deformed metamorphic rocks. Relying on King's notes, Hague described Archaean quartzites and crystalline schists extending from the crest all the way down to the valley to the west, where they disappeared under Pliocene sedimentary rocks. This situation continued to the northern end of the range. Aside from one or two small remnants, the Paleozoic limestone was gone.

Archaean quartzite, [East] Humboldt Range, Nevada (King 1878).

The next report published was Volume I, Systematic Geology (King 1878), an ambitious tome. Much of it was what we call historical geology—a challenging subject then. Some very basic geology had yet to be figured out, for example the composition of the Earth, and the origin of mountains.

Contractionists argued the Earth was a solid body that was cooling and contracting. Wrinkling of the shrinking surface created mountains. Others argued that the Earth's interior was molten; convection currents in the molten interior created volcanoes and other mountains. Clarence King leaned toward the latter hypothesis, but addressed it only briefly in his report. "I prefer to build no farther till the underlying physics are worked out ... leaving their minute discussion to a day in the near future when it can be done on a firmer physical foundation" (italics mine).

What was King thinking when he wrote "near future"? Years? Decades? In fact, it would be almost a century before geologists came up with plate tectonics, and another twenty years passed before "metamorphic core complex" was added to their vocabulary.

East Humboldt Range (Hague & Emmons 1877). Click to view geologist on an Archean "island".

King took it upon himself to discuss "the configuration and general relief of the area of the Fortieth Parallel at the close of Archaean time". It was here that he revealed his thinking about the creation of today's mountains. "Over the whole distance from the Rocky Mountains to western Nevada, in almost every prominent range, the contact may be observed between the Archaean and the Palaeozoic series. At times, Archaean summits are seen to rise above the level of the deposition of the Upper Carboniferous ..." King concluded the ancient rocks at the crests of today's mountain ranges were once part of Archaean ranges. Then the high peaks became islands in a Paleozoic sea.

The East Humboldt Range was a fine example: "The Humboldt was one of the greater Archaean ranges, and the subsequent Palaeozoic rocks are deposited unconformably, abutting against its steeply inclined flanks, leaving unsubmerged insular Archaean summits."

In the Archaean section of Systematic Geology, King included a map of Archaean rocks with a cross section. The excerpt below shows "Archaean bottom of the ocean in which Paleozoic sediments were deposited ...". Note that the high peaks of the East Humboldt Range were above sea level during deposition of the Wahsatch limestone.

From King 1878, click to view.

Today the Ruby Mountains/East Humboldt Range is considered a metamorphic core complex (MCC; also called core complex). MCCs are giant complicated structures, and it wasn't until the early 1980s that someone came up with a generally acceptable hypothesis.

Based on Peterson & Buddington 2014, DeCourten & Biggar 2017.

As shown above, MCCs include a dome of lower crustal metamorphic rock exposed to some extent at the surface. Above it are unmetamorphosed sedimentary rocks of the upper crust. These have been faulted, fractured, detached, and transported away from the crest of the dome. In other words, today's geologists think metamorphic rocks in the Rubies and East Humboldts came not from Archaean high peaks but from deep below the surface. This is very cool! It's not often we get to look at rocks metamorphosed by the great pressures and high temperatures of the lower crust.

The highly deformed metamorphic rocks and the undeformed sedimentary rocks are separated by a low-angle detachment fault. At the contact, the metamorphic rocks have been mylonized—highly deformed by very large shear strain. I would think giant moving chunks of rock could do just that, especially if the lower crustal rocks were a bit ductile from all the heat down there.

Mylonized (seriously scrunched) rock, East Humboldt Range. NV Highway 229 west of Secret Pass.

I first learned about MCCs on trip across the Great Basin about 15 years ago. In Broken Land (2003), Frank DeCourten described how it had taken him several decades to get up the nerve to visit one. "The complexity of these structures struck me as virtually incomprehensible." I felt the same way, but fortunately I had several guidebooks along on my trip last October.

MCCs are intimidating in part because they are so huge, too big to see. We can only glimpse bits of the various parts here and there. The best view of a MCC on my trip was not in the Rubies but the northern Snake Range. In the photo below, the very thin rock band is mylonite, marking the low angle detachment fault. Outcrops above it are fractured Paleozoic sedimentary rocks that moved eastward.

Snake Range north of US Highway 50 near turnoff to Baker, NV.

On the west side of the Ruby Mountains, the walls of Lamoille Canyon provide views of contorted metamorphic rocks of the lower crust, which domed up with formation of the MCC.

A glimpse of the interior of the Earth!

The upper canyon features a pegmatite dike–sill complex intruded into gneiss and marble.