# Geology

Source page: https://carsonriverresorts.com/explore/geology

Deep time · At the resort and within an hour

Volcanoes that stopped erupting four million years ago, a torn seam of crust that still heats the springs and rattles the valley, and the ice that cut this canyon and left the boulders the cabins sit on. Then where to go and put your hand on it.

## The mountains came first, and they came twice

The granite under all of this was made about a hundred million years ago, in
the roots of a volcanic arc, when the ocean floor was sliding down under
California and melting. It cooled a few miles underground and sat there for a
very long time.

The range you can see did not exist yet. The Sierra rose late — mostly in the
last five million years — and it rose the way a trapdoor rises, tilting west
along faults on its eastern side. That eastern edge is where Markleeville is.

## A torn seam, and it is still tearing

The Sierra does not simply end here. It frays into the Great Basin along a
belt of faults called the **Walker Lane**, which absorbs something like a
fifth of the entire movement between the Pacific and North American plates.
Everything else on this page follows from that one structure: the volcanoes,
the hot springs, and the earthquakes.

They are not historical. On **8 July 2021** a magnitude 6.0 earthquake struck
about twenty miles southeast of Markleeville, with more than four hundred
aftershocks in two days and rockslides that briefly closed Highway 395. Eight
days later the Tamarack Fire blew up. In this county, the summer of 2021 is
one story with two halves.

The Genoa fault, which makes the western wall of Carson Valley, last broke
roughly four hundred and fifty years ago at an estimated magnitude 7.5. Its
polished bedrock face is still exposed and you can drive to it.

## The skyline is a row of dead volcanoes

Highland Peak and Silver Peak — 10,936 and 10,820 feet — are not carved
granite. They are **rhyolite lava domes**. Raymond Peak is andesite. Round
Top, at 10,381, is the basaltic-andesite plug of a volcano that last erupted
about five million years ago.

What you are looking at from Highway 4 is not a mountain range with volcanoes
in it. It is the worn-down stumps of the volcanoes themselves, erupted through
the same torn crust between about six and four million years ago, then stripped
of everything softer by ice and water.

## Why they found silver, and why it ruined them

The Monitor and Mogul mines went in on ore that formed when hot fluid rose
through those volcanic rocks and altered them. There was silver in it. There
was also arsenic.

The ore here is **copper sulfosalt** — enargite, luzonite, famatinite — and
that mineralogy is the whole tragedy of Alpine County. Sulfosalt ore resists
amalgamation, the mercury process that had just made the Comstock the richest
place in America forty miles away. Same era, same kind of mountains, wrong
mineral. Ore had to be shipped to Swansea, in Wales, to be smelted at all. The
local roasting furnaces were never built big enough. The boom was over by the
1880s.

Markleeville is not Virginia City because of a crystal structure.

The last chapter of that story is **Leviathan**, where Anaconda took half a
million tons of sulfur out of an open pit between 1953 and 1962. Water still
oxidizes the sulfides it left, and the acid drainage is a federal Superfund
site today.

## Then the ice

The crest carried an ice cap through the Pleistocene, and the East Fork runs
through what it left: a genuine **U-shaped glacial canyon**, dropping over
Carson Falls into Silver King Valley.

You do not need to go looking for the evidence. The flat the cabins stand on
is a **river terrace of rounded boulders** — rock carried, ground and dumped
by ice and meltwater. The California Geological Survey notes that glaciers may
have sat in the Grover valley as recently as eleven thousand years ago, which
is nothing.

And the river's ending is stranger than its beginning: past Genoa the Carson
runs another hundred and thirty miles and then simply stops, in the **Carson
Sink** — no ocean, no outlet, the last surviving puddle of an ice-age inland
sea.

## Where to go and put your hand on it

**Under your boots, here.** The rounded-boulder terrace the property sits on.
Glacial outwash, and the reason the ground is flat enough to build a camp on.

**The volcanic skyline, from Highway 4 or 89.** Highland, Silver, Raymond,
Round Top — domes and plugs, not peaks.

**The color line, from the road — and from the resort itself.** Pale
granite basement below, dark andesite caps above. Once you have seen it you
cannot stop seeing it, and you do not have to leave the property to see it:
stand at Campsite 7 and look up from the river.

**Grover Hot Springs — the pool is heated by a fault, not by magma.** Rain and
snowmelt sink along fractures, warm against hot rock at depth, and rise
mineral-rich; the probable conduit is a splay of the Genoa fault itself. The
hottest spring runs between 128 and 146°F depending on the snowmelt, and the
pools blend hot and cold to something you can sit in. Look for the
**travertine** at the outlets — mineral the water sheds as it cools. Twelve
minutes.

**The Genoa fault scarp, near Walley's Hot Springs.** A polished, touchable
range-front fault. About forty minutes, and the only place on this list where
you can lay a hand flat on the actual break.

**Round Top and Elephants Back**, from the Carson Pass trailhead — volcanic
plugs that outlasted the mountains they were inside. Twenty-nine minutes to
the trailhead.

**Rust-orange staining at the old Monitor and Mogul workings.** That color is
the hydrothermal alteration itself: the process that put the silver there, and
the process that made it unsmeltable. Sixteen minutes to the pass.

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Carson River Resort · 12399 Highway 89, Markleeville, CA 96120 · (530) 694-2229 · store open 8am to 6pm, every day.
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