[1][2] The area was created as an addition to the National Wilderness Preservation System in 1994 as a part of the California Desert Protection Act.

In the early Cambrian, fossiliferous sediments from a shallow sea were deposited upon a basement of Proterozoic granite and later uplifted to form the Marble Mountains.

Deeper sediments were metamorphosed into quartzite and form a thin layer ~10 ft (3.0 m) thick between the shale and basement granite.

[4][5] The abundance of trilobite fossils, some measuring as long as 8 in (20 cm), give the wilderness area its name – in places virtually every piece of extracted rock contains pieces of fossil trilobite.

[7][5][4] In all, roughly 21 species of Cambrian invertebrates have been discovered in the area, including articulate brachiopods and Anomalocaris appendages.