What makes the Marble Mountains especially attractive to paleontologists is the comparatively rich Cambrian fossil biota which can be found in a particular rock layer, the Latham Shale, that is well-exposed in the southern part of the range, as well as in some nearby ranges such as the Bristol Mountains. The Latham Shale and the rock layers below and above it comprise a well-studied section of Lower and Middle Cambrian strata, which extends, with some variation, over a large part of the southern Mojave Desert. The dominant fossils in the Latham Shale are trilobites in the Olenellina. Olenellids, unlike almost all other trilobites, lack facial sutures, and the cephalon or head was molted as a single piece. Olenellid heads are common in the Latham Shale.
Complete trilobites are more rare.
Olenellids were restricted to the Early Cambrian, and the olenellids in the Latham Shale are relatively late in the group's history. Shown at left is a complete specimen of the genus Olenellus , probably O. clarki . Although trilobites are the most common and most popular fossils in the Latham Shale, they are not the only fossils that have been found there. Trace fossils left by worms and by trilobites are also fairly common. Fossils can also be found in the rock layers above and below the Latham Shale.