Latham Shale - California Dreamin'
A Latham Shale Trilobite Exposure
The scenic vistas are incomparable. Every curve in the road presents another postcard-perfect view of sky, sun and soil joining to form a colorful homage to the best that Mother Nature has to offer. Driving in air-conditioned comfort along legendary Route 66 towards Southern California's majestic Marble Mountains is an experience designed to equally stir the mind and soul. As the sun rises ever higher over these jagged, weather beaten peaks, its rays occasionally catch a crystalline outcrop, causing this impressive desert landscape to glisten like one of the planet's most precious jewels. In the minds of many, that's exactly what this rugged stretch of land located in the heart of the unforgiving Mojave Desert is… one of the most magnificent spots on the entire face of the North American continent.
In all honesty, however, despite its imposing majesty, to label the environs in and around this mountain range as merely “inhospitable” would seem to do injustice to the word. It's hot… it's dry… at times it's downright brutal. During peak summer months, midday temperatures will often reach 120 degrees, and local legend has it that eggs opened on any flat rock surface will cook through in less than a minute. The surrounding terrain, while certainly possessing it's own awe-inspiring grandeur, often appears as barren as an alien wasteland with the high altitude, rock-strewn landscape broken only by the occasional appearance of a sturdy California Barrel Cactus.
Here in the grasp of the desert, cars frequently overheat… as do any unwary occupants of those vehicles. The surrounding ring of majestic peaks, which occasionally reach up over 7,000 feet into the perpetually cloudless heavens, seems to further confine and magnify the sun's relentless intensity. It's all enough to create a potentially lethal environment for anyone brave -- or foolhardy -- enough to test the limits of this unforgiving spot of terra firma.
And the fact is that the inherent beauty -- as well as the inherent danger -- presented by this oft-challenging landscape has been part of the American consciousness for more than a century. Indeed, some 150 years ago, back when the Wild West was still at its rip-roaring peak, those who chose to trek through the Marble Mountains did so with either an impressive sense of determination, or little true awareness of what hardships lay before them.
To be honest, many of the same issues that faced those early travelers, especially those involving both the unrelenting heat and the corresponding scarcity of water, are still essential part of local lore. The stories of intrepid explorers who lost their lives to the ruthless elements remain as stark reminders to those who today choose to venture to this area in search of rock-climbing thrills or off-road adventures. Unquestionably, this is a demanding land, one of America's last great wildernesses, and located as it is just four hours southeast of Los Angeles, there are still plenty of hearty souls who remain eager to partake in the Marble Mountain's myriad natural charms.
Among those who flock to these mountains on a regular basis are a particularly dedicated group of visitors whose primary interest lies not merely in enjoying the range's rugged beauty. Rather, for these intrepid trailblazers their focus centers on pursuing the Paleozoic bounty housed within the various geologic formations that comprise the Marble Mountain's sedimentary layers.
At the core of these outcrops lies the 518 million year old Latham Shale, source for some of the most spectacular and important Lower Cambrian trilobites in the world. Featuring an exotic array of closely related species including Olenellus fremonti, Olenellus nevadensis and Bristolia bristolenis, the trilobites of the Latham Shale serve as exceptional examples of early life's first flowering on our planet. Usually two to three inches in length (but on occasion considerably larger) and wonderfully preserved in a thin, brown calcite that contrasts dramatically against the rust-hued limestone matrix, these are trilobites that emerged less than three million years after multi-cellular life initially exploded on earth.
Indeed, the rarity, beauty and importance of these fossils have long provided impetus for fossil-loving folks from around the globe to venture into this beautiful yet often inhospitable SoCal territory. Throughout the years thousands of trilobite specimens have been discovered within the Latham Shale's abundant layers, with many of those examples now filling shelves in both museum displays and private collections.
The Olenellids that emerge from these rocks represent an incredibly successful family of these ancient arthropods, with their fossilized remains being found everywhere from California to Pennsylvania to Scotland. Yet the fact is that whether due to their delicate external design, or the ever-shifting climactic and oceanic conditions that dominated this often-volatile stage of earth history, the Olenellids only appear in the fossil record for approximately five million years… a mere instant in geologic time. Thus the trilobites of the Latham Shale provide a very special look into what was occurring within the world's oceans more than half a billion years ago.
“The trilobites that come out of the Latham Shale are certainly among the most attractive and important Lower Cambrian examples anywhere,” said Richie Kurkewicz, a California-based collector of Cambrian species. “The entire area is so rich with trilobites, and a number of those layers have never been properly explored. Thankfully the Latham Shale has been worked for many years and the results of those efforts have provided science with a wonderful chance to see how early life was flourishing.”
There are a variety of fossil-bearing Cambrian layers housed within the Marble Mountains including the Middle Cambrian Chambless and Cadiz formations. Yet unquestionably the most renowned and studied geological component of this region is the 60 foot-thick exposure of Latham Shale that appears sporadically along the western slopes of the Providence Range, within which the Marble Mountains are a primary component.
In these Lower Cambrian layers, the easily fractured matrix produces trilobite parts in impressive numbers. In fact, within certain Latham strata disarticulated Olenellus cranadia can appear on virtually every extracted rock. The discovery of complete trilobites, however, especially examples of the rare Bristolia species, is still reason for a major celebration by any hammer-wielding adventurer fortunate enough to uncover one. And while the hunt for trilobites remains the clear focus of most collectors' energies, there are also a healthy assortment of other faunal elements to be found throughout the Latham - including abundant brachiopods and primitive sponges along with the occasional echinoderm.
As one might surmise, there has been a healthy degree of scientific speculation regarding why fragmentary trilobite remains so dominate the Latham Shale layers. Some experts have indicated that these deposits may represent a 500-plus million year old trilobite molting ground, a place where these primitive arthropods gathered on a regular basis to shed their thin calcite shells. Others have speculated that the strong offshore currents of the Panthalassic Ocean that surrounded the ancient supercontinent of Laurentia - and in which the trilobites that fill the Latham Shale once lived amid a series of shallow, cool water off-shore reefs -- served to tear apart fragile trilobite exoskeletons soon after their demise.
“If you contrast the faunal content of the Latham Shale with that of the Pioche Formation of Nevada, another outstanding Lower Cambrian site, the trilobite preservation is considerably different,” said Kurkewicz. “For whatever reason there are more complete trilobites found in Pioche, while Latham produces more fragmentary specimens. I think that evidence refutes the hypotheses that the quality of the trilobite's shell is the reason for them being torn about so easily in the California location.”
Unlike a number of other prominent western trilobite localities, such as British Columbia's renowned Burgess Shale, hunting for these fossils in the mountains of Southern California has a rather obscure and relatively recent history. Due to the intense climactic conditions that dominate the region, it is easy to understand why some scientists were initially hesitant to explore this harsh land. A variety of Native American tribes - including the Yuma, Serrano and Cahuilla -- have lived for centuries in close proximity to the Mojave Desert. Yet it wasn't until the early years of the 20th Century that Southern California's abundant Paleozoic formations began to draw a modicum of scientific attention. It was then that Nelson Horatio Darton of the United States Geological Survey first began investigating the area's Cambrian exposures, including the Latham Shale. In the process of doing so, he mapped the region's most prominent geological outcrops and gathered together a representative fauna - including an assortment of trilobite species.
After conducting some preliminary studies on his finds, Darton then proceeded to turn the bulk of his research, along with the corresponding specimens, over to the legendary Charles Walcott. At the time Walcott was widely considered the world's foremost expert on Cambrian fossils, and was then in his first years as the prestigious Administrator of the Smithsonian Institute. Somewhat ironically, Walcott incorrectly identified the Latham material as Middle Cambrian, which would have made it contiguous with another of Walcott's pet projects… the Burgess Shale, which was actually some 15 million years more recent.
In 1907, Darton decided to take matters back into his own hands by publishing a small paper in the Journal of Geology that outlined his Latham Shale discoveries, and clearly identified the material as being Lower Cambrian. In all honesty, at that time his efforts generated only a minimal impact on the scientific community. And it wasn't until after World War II, when subsequent teams of collectors started to make their own pilgrimages to the Marble Mountains in search of trilobites, that the site and its corresponding fauna began to receive its due-credit as a significant paleontological resource. Indeed, over the ensuing decades, a trip to the Marble Mountains became nothing less than a “bucket list” necessity for any American trilobite collector worth his weight in genal spines.
Yet despite the almost magnetic lure these layers have long held for collectors, as well as their lingering scientific importance, it seems that the Latham Shale is about to enter a challenging new chapter in its storied history. Due to the advent of recent legislation, much of the Marble Mountains' fossil-bearing matrix currently finds itself resting within the confines of what has been designated as the Mojave Trails National Monument. This jurisdiction places virtually the entire Latham Shale outcrop inside of a park controlled the Bureau of Land Management, a fact that greatly restricts the rock-breaking ambitions of anyone in pursuit of Paleozoic prizes. Indeed, much of the area is no longer open to digging by unauthorized visitors, and in recent days even those sporting haughty museum credentials have been turned back, or at least delayed, in their efforts to further explore this hallowed ground.
We all can forever argue whether such restrictions, well intentioned or not, truly benefit the preservation of natural resources… or if they are merely an unwanted and unnecessary infringement on citizens' right to use public lands. Indeed, it seems that there is a growing trend throughout the nation (and the world) where ever-increasing government restrictions are being imposed in an effort to best preserve fossils and minerals that are perceived, or at least categorized, as national “treasures”.
However, the fact is that even with these recently instituted laws going into effect, a full complement of material has long-since been culled from the Latham Shales' Lower Cambrian layers, providing fossil enthusiasts with an abundance of opportunities to continue learning about this unique Paleozoic outcrop. Even if collectors can no longer break apart these ancient shale layers, California's rugged Marble Mountains will always remain a worthy, if challenging destination for anyone interested in uncovering evidence of life's initial efforts to establish a tenuous hold in the primal seas of Planet Earth.
“The Latham Shale material certainly did not initially trigger the degree of scientific interest of, say, the Burgess Shale,” said Kurkewicz. “But its stature within in the paleontological community has clearly grown throughout the years. Subsequently, many of the finds made in the Marble Mountains have allowed us to gain an ever-greater understanding of some of the first trilobites that ever emerged.”