Marble Mountain Wilderness in northern California

Marble, with its typical brilliant white color, is beautiful! And it’s rare on the U.S. west coast. So I was excited to finally visit the Marble Mountains in northern California via a backpacking trip from July 13–16. Five of us traveled 2 hours south from Ashland, Oregon, and parked at the Lovers Camp trailhead. From there, we hiked up to Marble Valley and set up our camp. We then had several days to hike around with only our day packs.

Hiking up toward Marble Gap between Marble Mountain (left side) and Black Marble Mountain (not visible—see other photo of the gap below). The gleaming white rock is marble.

What is marble?

Marble is a metamorphic rock that forms when limestone (a sedimentary rock) is buried deep beneath Earth’s surface where elevated temperatures and pressures cause carbonate minerals (calcite, aragonite, dolomite) to recrystallize. Limestone is a biological type of sedimentary rock—it consists of organisms’ hard parts that range from tiny single-celled algae and animal plankton to mollusks such as clams to large coral reefs. Most limestone forms in the ocean, so when we find this rock on land it means the land was once covered by ocean water or that pieces of oceanic crust with overlying limestone rock was accreted (added) to the continent.

Limestone is abundant in the mid-west and eastern parts of the U.S. Most of those rocks were deposited during times in the Paleozoic and Mesozoic Eras when the continent was flooded by the ocean. Limestone is less common along the U.S. west coast—at most of these locations oceanic crust was added to the continent during hundreds of millions of years of plate tectonic activity related to the subduction of oceanic plates and their accretion onto continental plates.

The Klamath super-terrane

The Marble Mountains are part of the very complicated area between Reading, California and Roseburg, Oregon called the Klamath terrane. A terrane is a crustal block that is bounded by faults and displaced from where it originally formed. The Klamaths are a “super-terrane” because they are an amalgamation of many separate terranes.

Geologic map of Klamath Mountain terranes. The Eastern Klamath terranes are the oldest—reaching back >500 million years ago. Terranes are progressively younger to the west, with most of the action occurring during the Mesozoic Era, when the whole collection of terranes docked with the continent. The terranes consist of metamorphic volcanic and sedimentary rocks of oceanic origin. The red blobs are intrusive bodies (e.g., granite), most of which intruded into pre-existing rocks during the Jurassic Period about 160 million years ago. These bodies include the Ashland pluton—the red blob located just south of Medford, Oregon.

The Marble Mountain Wilderness is in the Rattlesnake Creek terrane (white cobbled pattern) that is part of the Western Klamath belt of high-grade metamorphic rocks. The north end of the wilderness is located about 50 km (30 miles) west, and a little south, of Yreka. Map is from Stokes and Barnes, 2006 (see reference below).

The Klamath group of terranes has a long and complicated history. In a blog post about my local region around Ashland, Oregon, I provided a brief introduction to these mountains: Basically, the Klamaths consist of a vast variety of oceanic materials, including all parts of the oceanic crust and overlying marine sediments. These oceanic pieces were accreted to each other and then to the continent via a long history of subduction that included colliding volcanic islands.

Making the Marble Mountains

The terranes of the Klamath Mountains are separated by thrust faults (black lines with small triangles on map above), as shown on the cross section below.

This cross section across the Klamath Mountains is located to the north of the Marble Mountains, but it shows how terranes are separated by thrust faults that create east-tilting blocks. The blocks are progressively younger to the west and have been shingled by the action of faults that thrust older rocks to the east over younger rocks to the west. The Marbles are part of the Western Paleozoic and Triassic terrane. Figure is from Alt and Hyndman, 2016 (see references below).

Before it was metamorphosed, marble was limestone. Shells of organisms on the seafloor created limestone rock overlying oceanic crust formed by volcanic (magma erupted on the seafloor) and plutonic (magma cooled beneath the seafloor) processes. Because of the high metamorphic grade, very few fossils are preserved. The limestone probably formed in a reef around a volcanic island that was located closer to the equator and that traveled eastward and northward with an oceanic tectonic plate. When the plate encountered a subduction zone, pieces of the plate and the overlying sedimentary rock were accreted to the continent through a complicated series of collisions.

Components of the Marble Mountains

The marble rocks are tilting toward us in this westward view of Marble Mountain (left side of photo) and Black Marble Mountain (right side of photo). Black Marble Mountain is misnamed because the black color is schist that is faulted over the underlying white marble. Schist is metamorphosed marine mudstone.
This location on Marble Mountain shows dark-colored igneous rock intruded into the white-colored marble. The igneous rock is dark in color because it has a mafic composition. This means it has abundant iron- and magnesium-rich minerals and a low amount of silica. This is not surprising because the rocks that make up oceanic crust are mafic in composition.
The Marble Mountains were probably named this because the white color of the marble is so distinctive in the landscape. However, most of the rocks have other oceanic origins. This view is of Sky High Lakes, a popular camping and hiking destination. The prominent ridge is composed of pieces of igneous oceanic crust, including serpentine. The iron-rich mafic rocks commonly weather to a reddish color.
Not all of the white rocks are marble. The white rock in this photo is quartz that forms a vein in the metamorphic schist rock. During the process of metamorphism, silica-rich fluids pass through pre-existing rock and crystallize to create quartz in fractures.
This view is southward over the marble rocks to other mountain ranges in the Klamaths. The distance peaks are in the Trinity Mountains located northwest of Redding, California.

Caves and flowers

You may be aware that most caves are formed in limestone (or marble). This is because of chemical weathering: carbon dioxide in the air dissolves in rainwater to form weak “carbonic acid” that dissolves limestone as it seeps into cracks and cavities. Sure enough, there are abundant caves in the Marble Mountains. One of my former colleagues at San Francisco State University studied these caves (Davis and Serefidden, 2004, see reference below), and I have been wanting to visit these mountains since he told me about them many years ago.


Barb, Mary, Margaret and Esther—the other 4 members of our backpacking team. Barb called us the “Marble Mavens”!

For photos of other beautiful marble rocks, visit my post about the famous Carrera marble quarry in northwestern Italy ( This marble block is much larger than California’s Marble Mountains and more accessible for quarrying.

Other beautiful carbonate rock are found in Italy’s Dolomite Mountains. To view photos of the Dolomites, see my posts in September 2022 (e.g., These rocks were altered by fluids with magnesium that changed the original calcite (CaCO3) into dolomite [CaMg(CO3)2].


Davis and Serefiddin, 2004, The Marble Mountains of northern California: Alpine Karst journal.

Stokes and Barnes, 2006, The development of plate tectonic concepts for the Klamath Mountains province, California and Oregon: GSA Special Paper 410.

Alt and Hyndman, 2016, Roadside Geology of Northern and Central California: Mountain Press.

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  1. Lynn on July 31, 2023 at 11:20 pm

    Studying wine regions throughout the world is helpful… I understand a fair amount of your share. And now I know more about marble ;-). Side note- many buildings and houses in Pau have marble floors from the nearby quarries. (The house we were supposed to buy had one.)

    • Landscapes Revealed on August 1, 2023 at 5:15 pm

      Nice! Today we visited Abacela winery, which has an interesting geologic setting on a major fault. Sounds like I’ll need to visit the marble quarries near Pau when we visit you sometime. Hope you find another house with marble floors!

  2. Maria on August 1, 2023 at 7:31 am

    Nice to learn the origin of the Marbles after hiking there so many times.

    • Landscapes Revealed on August 1, 2023 at 5:13 pm

      Thanks for reading Maria!

  3. Keeley Kirkendall on August 1, 2023 at 9:19 am

    Excellent. Thanks!

    • Landscapes Revealed on August 1, 2023 at 5:15 pm

      Thanks for reading Keeley!

  4. Paul on August 1, 2023 at 9:49 am

    I have spent a good portion of my career learning from geologists and the education you provide in “landscapes-revealed” never disappoints. Your Marbles report brought to mind a geology question that I have regarding an area about 30 miles East of that range. Is there any way I can ask you my question and perhaps send some pictures?

    • Landscapes Revealed on August 1, 2023 at 5:16 pm

      I’ll send you an email!

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