Scenes From Fossil Insect Canyon

Mojave Desert, California

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Parked along the non-maintained dirt trail in the midst of Fossil Insect Canyon. Within this view, colorful but organically barren volcanic rocks practically engulf the fossiliferous horizon. Only that narrow pale brown strip of the 17 million year-old middle Miocene Barstow Formation at roughly upper left, lying just below the reddish-brown dacite extrusives, contains common to abundant calcium carbonate concretions, within which a genuine paleo-bonanza of fossil insects, arachnids, crustaceans, and even diatoms can be dissolved free of their calcareous matrixes. In order to reach most of the paleontologically significant outcrops of the Barstow Formation in Fossil Insect Canyon, visitors must hike well away from the main trail through rugged, unforgiving Mojave Desert terrain.

Here is the stuff paleontological dreams are made of--one of the ne plus ultra, prime, fossil localities in the middle Miocene Barstow Formation, as exposed in Fossil Insect Canyon. The sediments seen just below the reddish-brown igneous dacite yield distinctive calcareous concretions of varying sizes and shapes--from approximately a quarter inch (6 millimeters) to three inches (7.6 centimeters) in diameter, within which occur beautifully preserved three-dimensional freshwater arthropods.

Typical rugged topography in Fossil Insect Canyon. The low-lying sandstones and siltstones in the immediate foreground are notably unfossiliferous, unfortunately, lying as they do close to an unimproved dirt trail through the canyon corridor. Here, one must hike into the badlands to find the fossils, to the pale-brown to pale-greenish outcrop in the upper right quadrant of image, below the distinctive reddish-brown slope of volcanic dacite. The hike is well worth one's effort, obviously.

Volcanics and sedimentary rocks of the middle Miocene Barstow Formation lie jumbled together in a dramatic, colorful outcropping along the trail through Fossil Insect Canyon. No rocks within this view are fossiliferous, by the way.

My late father's CJ7 jeep is parked along the unimproved road through Fossil Insect Canyon. Authorities no longer maintain the road, by the way--visitors must proceed at their own risk. Sedimentary exposures nearest to the road here are unfortunately unfossiliferous--although that rather nondescript, narrow ledge of siltstones just below the overlying reddish brown volcanic dacites (dated radiometrically at around 16.8 million years), in upper one-quarter of image, contains fossil-bearing calcium carbonate concretions in the middle Miocene Barstow Formation (here, around 17 million years old).

A wonderful exposure of the Cenozoic rocks present in Fossil Insect Canyon. The fossil-yielding section lies near the prominent ledge in upper half of image, below the reddish-brown igneous dacites which cap the local geologic sequence.

A vista across the middle Miocene Barstow Formation (whitish-brown mudstones, siltstones and calcareous sandstones in immediate foreground) to a mountain composed of the volcanic, unfossiliferous dacite flows.

Badlands outcroppings of the middle Miocene Barstow Formation in Fossil Insect Canyon in immediate foreground--here unfossiliferous, by the way, although several beds of extremely fine-grained calcareous sandstones yield excellently preserved ripple marks and paleo-currents, demonstrating deposition in rather shallow lake waters in this portion of the stratigraphic sequence.

Here occurs one of the more fantastically fossiliferous sections of the middle Miocene Barstow Formation in Fossil Insect Canyon. Practically all the pale-greenish microlaminated shales in roughly center of image, lying below the volcanic dacite cap, contain numerous calcareous concretions, within which a bounty of insects, spiders, crustaceans and even diatoms can be recovered in three-dimensional glory from the insoluble residues of a diluted acid bath.

One of the major dry tributaries to the main wash through Fossil Insect Canyon. Many abandoned exploratory mine tunnels can be observed in this area. They are completely unsafe and must never be entered. None of the sedimentary rocks in this particular view yields fossil-bearing calcareous concretions, it should be noted.

Here occurs another bonanza locality--where abundant fossiliferous calcium carbonate concretions occur in the microlaminated shales that lie several feet below the reddish brown volcanic dacite cover at the skyline.

A special note here: Practically every major concretion-producing horizon in Fossil Insect Canyon has been heavily prospected through the decades by amateur fossil enthusiasts and professional paleontologists alike. Literally hundreds of thousands of such calcium carbonate stones have been removed from the canyon since their precious fossil "cargo" was discovered during the mid 1950s. It is hoped that visitors to the district will take home only a modest number of concretions, leaving intact the integrity of the stratigraphic sequence for others to study and enjoy. Otherwise, officials will doubtless close the canyon to all but professional paleontologists bearing a degree from an accredited university.

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