Marble Mountains

This trip ventures into southeastern California and the Mojave Desert with stops along I-40 and U.S. 66 at the Marble Mountains, Amboy Crater, and the Kelso Sand Dunes.

Figure 1: Labeled are the four main stops along the Marble Mountains Field Trip.

The following road map will show the stops on the trip (Figure 1). The Marble Mountains are south of I-40 near the town of Cadiz, California where the “Lower Paleozoic Section” is labeled.

The first point of interest on the trip towards the Marble Mountains is on I-40 about 20 miles west of Needles, CA. The first pass (Sacramento Pass) outside of Needles consists of Precambrian gneiss and schist that are exposed along the road cuts (not on the map). Entering the next valley, there is a distinctive light gray and dark brown mountain ahead in the distance and north of I-40 (Figure 2). As this mountain is approached, more detail is noted (Figure 3). The light gray underlying the dark brown is granite that has shot dikes upward and into the dark brown material. The dark brown material is pre-existing country rock in which the granite intruded. This is a classic roof-pendant that has been uplifted and exposed, rather spectacularly.

Figure 2: Distant view of the roof pendant showing the lighter colored granite overlain by dark country rock into which the granite intruded.

Figure 3: Close-up view of the roof pendant displaying granitic dikes intruding into the dark country rock.

Figure 4: Permian limestone in almost vertical position at Mitchell Cave State Park north of I-40.

The Marble Mountains in the Mojave Desert of eastern California are a part of a much greater expanse of Paleozoic strata that have been folded and tilted in the region. North of I-40 in the Providence Mountains and at Mitchell Caverns State Recreation Area are partially composed of late Paleozoic limestones (Pennsylvanian and Permian) that have been tilted in some places almost vertically (Figure 4). Fusilinids, single-celled organisms from about ¼ to ½ of an inch long, are present in the limestone.