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Alaska Miners Association Phone: 907-563-9229 Fax: 907-563-9225 ama@alaskaminers.org www.alaskaminers.org ELKO / Mining Expo Phone: 775-738-4091 Fax: 775-738-2420 jennifer@elkocva.com www.exploreelko.com WorldWide Drilling Resource ® is proud to be a member of these mining associations. Northwest Mining Association Phone: 509-624-1158 Fax: 509-623-1241 nwma_info@nwma.org Women in Mining 866-537-9694 wim@womeninmining.org 53 WorldWide Drilling Resource ® JUNE 2013 The Barstow Syncline by Harry W. Short Engineering Geologist The Barstow Syncline is a geolog- ical basin structure located approximately eight miles north of Barstow, California, in the Mojave Desert. It is also a National Natural Landmark. The Rainbow Basin is a mixture of private and public land managed by the Bureau of Land Management. The basin is notable for its syncline and the fantastic, beautiful shapes of its rock formations. The fossils in these beds have provided scientists with valuable information about life dur- ing the middle Miocene epoch, between 13 and 18 million years ago. The Rainbow Basin is underlain by a massive batholith that lies below much of the Western Mojave and is composed of a rock type named quartz monzonite. This structure is Cretaceous, or possi- bly the late Jurassic period. Early in the Cenozoic era, this batholith was exposed in the area surrounding Rainbow Basin and underwent compression due to tec- tonic activity and formed a geologic basin whose multicolored rocks are visible in the Barstow Syncline. Differential erosion has beautifully sculpted the colorful for- mation sediments into their fantastic shapes. The thick sedimentary rocks in the syncline have been divided into three distinct formations. The lowest is called the Jackhammer Formation composed of layers of sandstone, siltstone, lime- stone, and conglomerate which dates back to the early to middle Tertiary period. Above this is the Pick Handle Formation composed of volcanic tuff, rhyolite, and breccia. The highest of the three formations is the Barstow Formation made of layers of conglomerate, limestone, and sand- stone which dates back to the middle to late Miocene. It contains one of the largest Cenozoic fossil assemblages in North America which includes camels, horses, mastodons, and flamingos. Most of the sediment that makes up the layers in this formation were stream deposits. There is a white layer of rhyolitic tuff called a marker bed due to its promi- nence near the top of the formation. Finally, overlying the syncline is a layer of late Pleistocene age (during man’s time on earth) alluvial deposits. To get there, take Main Street in Barstow to First Avenue, cross the rail- road tracks and the Mojave River to Fort Erwin Road, then turn left at Fossil Hill Road. The Rainbow Basin is open to the public by means of a one-way dirt road that loops through the basin. Camping is allowed in nearby Owl Canyon Campground. Fossils cannot be collected without a permit. Anyone plan- ning a trip to this natural landmark should keep in mind it is a desert area, and take appropriate safety precautions. Please take care of my favorite geo- logic place by not destroying Mother Nature’s beautiful creations. Do like the cavers - take nothing but pictures, and leave nothing but footprints. Harry Harry Short may be contacted via e-mail at editorial@ worldwidedrillingresource.com 4 *+ .* *..*( ,$''$)" **'- !--*,$!-5 111 %!).! # ,$''$)"-/++'3 *( !,0$)" .#! ($)$)" $) /-.,3 .#,*/"#*/. .#! 1!-. ((!,- $.- ,$'' .!!' / - ,$''$)" '/$ - #,! *(+*/) - !1 !,/) *. ,3 $.- $. $+! ) '$)" **'- )"!)/$.3 ,$0! + ,&- !0 #*)! !-. $) .,!!. '&* !0 2