A chunk of limestone from the Lower Cambrian Chambless Limestone bearing dark oval nodules called Girvanella, an extinct genus of blue-green algae precipitated by cyanobacteria. The fossils were collected from the classic trilobite quarry in the Marble Mountains long before that area became part of a national monument.

The Marble Mountains trilobite locality presently lies within Mojave Trails National Monument (officially authorized and established on February 12, 2016), where the BLM (Bureau of Land Management) continues to allow the casual collection of reasonable amounts of common invertebrate fossils--a designation that here includes trilobites; for fossil sites situated on private property, visitors must secure explicit permission from the land owners.