Marble Mountains Trilobite Quarry in Cadiz, California

The Marble Mountains, in California’s Mojave Desert, contain extensive exposures of Cambrian sedimentary rocks. The Cambrian is the oldest unit of the Paleozoic era, extending from about 540-490 million years ago, and is famous as the time when macroscopic fossils with “hard parts” first appeared. The most characteristic fossils of the Cambrian are trilobites, creatures distantly related to insects and crustaceans. Typically they consist of a mineralized head part (the "cephalon"), with segmented middle and tail parts. Because of its size and mechanical resistance, the cephalon tends to be the most easily fossilized part. Trilobites are abundant in the Cambrian rocks, particularly in a greenish-rusty colored shale traditionally called the Latham Shale. In fact, much of the northern part of the range is included in the Trilobite Wilderness Area. The most convenient area to search for trilobite fossils, however, is at the southern tip of the mountain range, where there is a de-facto quarry where the public is welcome to dig for fossils. (Within reason, of course; don’t bring a backhoe!)

May 23, 2025 - 18:02
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Marble Mountains Trilobite Quarry in Cadiz, California

View southwest from the trilobite quarry out to Cadiz Valley.

The Marble Mountains, in California’s Mojave Desert, contain extensive exposures of Cambrian sedimentary rocks. The Cambrian is the oldest unit of the Paleozoic era, extending from about 540-490 million years ago, and is famous as the time when macroscopic fossils with “hard parts” first appeared.

The most characteristic fossils of the Cambrian are trilobites, creatures distantly related to insects and crustaceans. Typically they consist of a mineralized head part (the "cephalon"), with segmented middle and tail parts. Because of its size and mechanical resistance, the cephalon tends to be the most easily fossilized part.

Trilobites are abundant in the Cambrian rocks, particularly in a greenish-rusty colored shale traditionally called the Latham Shale. In fact, much of the northern part of the range is included in the Trilobite Wilderness Area.

The most convenient area to search for trilobite fossils, however, is at the southern tip of the mountain range, where there is a de-facto quarry where the public is welcome to dig for fossils. (Within reason, of course; don’t bring a backhoe!)