Chambless Rock Collecting Area

BLM Route NS328 leaves National Trails Highway just west of Chambless and runs north toward the Marble Mountains. About two miles up the route the Chambless Rock Collecting Area opens on both sides of the road. The Bureau of Land Management’s Needles Field Office manages the ground, and Recreation.gov places it near Essex. Collectors come for hematite and magnetite, which lie in reddish-brown iron deposits near old mining shafts, and for green epidote, which turns up in the washes.

Garnet, epidote and a gray ridge

The BLM’s own description of the area reads like a short itinerary. An abandoned quarry yields sizable chunks of limestone and marble. Epidote is scattered about, and much of it holds bright metallic hematite blades. Tiny garnets with dark red and brown crystals lie in the adjacent canyons. Farther east, in another canyon, a gray ridge of limestone is embedded with many fossils.

The agency’s general rule on its public lands lets visitors take reasonable amounts of rocks, mineral specimens, and semiprecious gemstones for noncommercial purposes, meaning the collector is not selling them for a business or for gain. Collecting is generally not allowed on developed recreation sites, on lands with active mining claims, or where the mineral estate is privately owned. Fossils fall under a separate rule. Under the Paleontological Resources Preservation Act of 2009, casual collection of common invertebrate fossils is allowed in the Mojave Trails National Monument, including the Marble Mountains. A BLM flyer from February 2017 defines casual collection as a “reasonable” amount for non-commercial personal use, gathered from the surface or with non-powered hand tools. The disturbed ground may be no larger than one square yard. The same flyer warns that private lands lie in and near the Marble Mountains and that it is the visitor’s responsibility to know where they are.

The range on the boundary

The collecting area sits on the southern boundary of the Trilobite Wilderness, which covers the Marble Mountains. Wilderness Connect describes them as a narrow volcanic range running 12 miles. Alternating dark brown and light brown striations, tilted by geologic processes, give the range its marbled look. Through its center stand several yellowish sandstone peaks with long talus slopes. East of the range the wilderness takes in low rolling hills and sloping bajadas. Creosote bush scrub and desert wash scrub cover the ground. Coyote, black-tailed jackrabbits, kangaroo rats, quail, roadrunners, red-tailed hawks, prairie falcons, rattlesnakes, and several kinds of lizards live there. A permanent population of bighorn sheep was last estimated at around 150, and the eastern part of the wilderness is critical habitat for the threatened desert tortoise. Motor vehicles, bicycles, carts, and other mechanical transport are generally prohibited inside the wilderness line.

The wilderness lies in San Bernardino County, about 60 miles west of Needles, between Interstate 40 and historic Route 66. The California Desert Protection Act of 1994 designated it on October 31 of that year at 31,160 acres. Most of the Marble Mountains now lie either in the wilderness or in adjacent Areas of Critical Environmental Concern. The southern part of the range, including the Golden Cycle district around the Castle Mine, belongs to the Mojave Trails National Monument.

Shafts, pits and the Trilobite mine

The shafts beside the iron deposits are older than any of these designations. A 2023 review by David C. Buesch and Bruce W. Bridenbecker of the U.S. Geological Survey dates active mining in the Marble Mountains to the earliest 1900s. Over the following decades it dwindled, and by 1959 only a few mines were still working. Most of the work was hard-rock. A few mines were small open pits, a few had a shaft or two with some adits, and most were a single shaft or adit. There were also several small open-pit marble mines and one open-pit fossil mine.

The authors measure the range as a block 10 by 30 kilometers, tilted gently to the northeast. Its western slopes expose Proterozoic plutonic and metamorphic rocks, Paleozoic sedimentary rocks, and Jurassic granitoids. Miocene volcanic and sedimentary rocks cap the crest and the eastern slopes. Ore formed around the edges of intrusions, along dikes, in carbonate rock, and along thrust faults. That process left gold, copper, malachite, azurite, bornite, chalcopyrite, magnetite, specularite, limonite, quartz, epidote, actinolite, and garnet. No rock or mineral mine in the range is active today. The Iron Hat mine and the Trilobite mine area are privately owned, but the Trilobite mine at the south end of the range is still open to the public.

Trilobites near the Cadiz siding

The range’s fossils entered the scientific record along a railroad. In 1907 N. H. Darton described the lower Cambrian rocks at the south end of the Marble Mountains as part of a study of the geology along the Santa Fe Railroad. According to Jack D. Mount, writing in the Bulletin of the Southern California Paleontological Society in December 1976, this was the original discovery of fossil-bearing lower Cambrian rock in the Mojave of eastern San Bernardino County. The site lay about 3.3 kilometers northeast of the railroad siding of Cadiz. Clark described the section in more detail in 1921 and listed four trilobite kinds. Working from Clark’s collection, gathered near the old Vaughan Quarry at the end of the Marble Mountains, Resser prepared the first systematic report in 1928. He described six taxa, three of them new olenellid trilobites.

J. C. Hazzard, working toward graduate degrees at the University of California, published a series of papers between 1933 and 1954 that named the area’s rock units. One of them carries the town’s name. Hazzard’s Chambless Limestone is 36 to 66 meters of massive gray limestone crowded with countless algal oncolites, with thinner beds holding trilobite fragments, brachiopods, and primitive mollusks. Beneath it lies his Latham Shale, 15 to 45 meters of shale, siltstone, and sandstone. Mount found the Latham dominated by olenellid trilobites, and he reported a new species of Anomalocaris and a new annelid from it, a pairing he called “reminescent of the Burgess Shale fauna.” His 1976 report figured 29 Early Cambrian fossils from these rocks, more than triple the number known before his studies began. The shale weathers to red, paper-thin fragments.