Paleozoic Outcrops in Mojave Desert

Donald Kenney (donaldkenney@gmail.com)
Last Update: Tue Jan 24 20:31:21 2017



Introduction

Mojave Desert Paleozoic

This is one of a series of "site descriptions" that I will be creating for classic fossil sites in the Eastern part of the region. This entry has to do with Paleozoic outcrops in the Mojave Desert of California. This writeup covers the following localities from my site list. CA0299,CA0300,CA0301,CA0304,CA0305,CA0308,CA0309,CA0311,CA0312,CA0313,CA0314,CA0315,CA0320,CA0321,CA0324,CA0325

The Site(s)

The Mojave is mostly covered by Miocene volcanics and Pleistocene fill, but there are a significant number of Precambrian through Permian outcrops in the Eastern Mojave. By far the best known of these is in the Marble Mountains about 80 kilometes (50 miles) East of Barstow.

The Marble Mountains are a low range of typical rugged Basin and Range type mountains in San Bernadino County, CA. Geographically, they probably are not in the Basin and Range Province. Drainage such as it is, appears to be SouthEast to the Colorado River thru a series of dry lakebeds. The mountains run roughly North-South about 50 miles West of Needles,CA and 50 miles East of Barstow, CA.

Geology

The Northern parts of the range consist of unfossiliferous(?) Tertiary volcanics, but at the South end there are several large blocks of Paleozoic material. These are tilted down on the Eastern/Northern sides and expose many hundreds of feet of Lower Cambrian through Permian material on their Southern/Western sides. The Lower Cambrian Wood Canyon, Zabriskie, Latham, Chambless, and Cadiz formations are well exposed in a number of places. The Latham Shales and overlying Chambless Limestone have abundant Lower Cambrian fossils. A few Middle Cambrian fossils can be found in the Cadiz Formation -- especially just below it's boundary with the cliff forming Bonanza King Dolomite. Above the Bonanza King are thin Upper Cambrian and Devonian formations, an unfossiliferous Pennsylvanian Limestone, and finally, the Permian age Bird Spring Limestone. The Upper Cambrian and Devonian beds are located high up a more or less vertical cliff and have not, to my knowledge, been much investigated. Fossils are present in the Permian age Bird Spring formation although the only outcrop I personally have visited is a few miles to the SouthEast on the edge of the Ship Mountains.

The beds in the Marble-Ship Mountains area are the Southwesternmost extension of what was probably a continuous area near shore marine deposits in the Lower Cambrian that extended North and East to cover Easternmost California, the Southern half of Nevada, much of Arizona, much of Utah, and parts of Idaho, Washington, British Columbia, and Montana. Beds tend to be older in the West. In particular, the Zabriskie Quartzite which is only a few meters thick in the Marble mountains is many hundreds of meters thick a few hundred kilometers to the North in Death Valley. The nomenclature of the formations also changes. The lowest formation exposed in the Marble Mountains is the Wood Canyon formation which corresponds to the Prospect Mountain Quartzite in Central Nevada and the Tapeats Sandstone of the Grand Canyon. The Latham-Chambless-Cadiz nomenclature is used only in the Southwestern area where the Chambless contains discrete limestone beds several meters thick. These thin to the North and East and eventually peter out whereupon the Lower-Middle Cambrian beds are termed the Carrara Formation. Further East the corresponding beds are the Pioche Shale or the Bright Angel Shale of the Grand Canyon region. Latham-Chambless-Cadiz exposures are found in the Providence Mountains, New York Mountains, Salt Spring Hills, Mesquite Range, and at a location described as "Northwest of Kelso" that I have never been able to identify. The Providence and New York Mountain exposures are in the Mojave National Preserve and are presumably closed to collecting.

Formations (youngest first)

Maps

Modified from https://ngmdb.usgs.gov/ngm-bin/ILView.pl?sid=41_1.sid&vtype=b

Stratigraphic Section

[http://web.archive.org/web/20070711134404/http://members.cox.net/jdmount/cambmojave0001.JPG]

Location

As a first approximation, there are several collecting areas in the Marble Mountains:

Paleontology

Rules and Access

See https://web.archive.org/web/20130601213542/http://www.blm.gov/ca/st/en/prog/wilderness/wa/areas/trilobite.html

All areas require driving on unmarked, unmaintained, desert, roads. These are generally navigable by passenger cars on the flats although sand and occasional rocks may be a problem for modern low-slung vehicles. The roads deteriorate substantially as they climb up into the mountains and really are accessible only to vehicles with high clearance and preferably with four wheel drive. All areas are within a twenty minute hike of places where most passenger cars can navigate successfully

As of April 2010, the exposures North of National Trails Highway (US66) lie within a "Trilobite Wilderness Area" declared in 1994. Exposures South of National Trails Highway including the area around the old Marble Quarry are several miles South of the Wilderness area as described on the BLM web site. Even within the Wilderness area "rockhounding" is described as a permitted activity and travel on existing roads is permitted as is camping for up to 14 days in the setback areas along the roads. In practice, non-commercial fossil collecting seems to be permitted. I chatted with a BLM Ranger out there in 2007 and was not made aware of any restrictions. The Wilderness area legal description is designed to be manually plotted on a topographic map (with contours in metric). Here's a rough map of the area which is formally described in [https://web.archive.org/web/20081012023322/http://www.blm.gov/ca/pa/wilderness/wilderness_pdfs/legal_descriptions/trilobite.pdf This link is no longer accessible on the web site and may not be an accurate description of the wilderness area boundaries..

I apologize for any errors and strongly recommend that anyone planning to engage in activities legal outside the wilderness area but illegal within plot the boundary themselves before acting.

The nearest supplies may be in Amboy 16km to the West which historically has had gasoline and a motel. However, stores, gasoline stations and such are not reliable in this region as they often close when the owner dies or retires. The nearest towns with substantial populations are Needles, Baker, Barstow and Twenty-nine Palms. All are at least an hours drive and parts of the road between National Trails Highway North of I40 and Baker are in extremely poor shape. It is important to carry drinking water and to have adequate gasoline. Radio reception is iffy. There was cell phone coverage near the old marble quarry on my last visit to the area in 2007, but because the topography is rugged one probably can not count on coverage in all areas.

Vegetation is sparse, firewood dubious. Wildlife is sparse, and potentially hostile. Rattlesnakes occur as do scorpions. Coyotes may threaten pets. There are no reliable springs or other water sources. Winter temperatures are pleasant although nights can be near or below freezing. Summer temperatures are life threatening -- often 110 degrees or more. There are people living in the area, but you may need to walk several miles if you get into trouble.

Related Localities

Although a few Middle Cambrian and Permian fossils are found in the area, the principle attraction is Lower Cambrian fossils in the Latham Shale and in shale beds in the overlying Chambless limestone.

References

Copyright, Licensing, and such

Copyright 2010 Donald Kenney (Donald.Kenney@GMail.com). Unless otherwise stated, permission is hereby granted to use any materials on these pages under the Creative Commons License V2.5 see http://creativecommons.org/licenses/by/2.5/.

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