Sierra Madre

A topographic feature often has two or more names, depending upon who saw it and from what view. Sierra Madre is the name applied in Wyoming to a section of mountainous terrain that is continuous with a mountain mass in Colorado called the Park Range. The Sierra Madre are the western prong of the Colorado Front Range that projects into Wyoming. This uplift separates the Saratoga Valley from the Washakie Basin, and may be structurally connected to the Rawlins uplift to the north. The crest of the Sierra Madre is the Continental Divide, and the highest point is Bridger Peak (11,007 feet). Drainages on its west flank flow to the Colorado River by way of the Little Snake River; drainages on its east flank flow to the North Platte River.

Geologically, the Sierra Madre are quite similar to the Medicine Bow Mountains, but lack the broad upland surface of the latter. The same major shear zone (or suture) that cuts across the Medicine Bow Mountains is also present in the Sierra Madre. This suture, called the Cheyenne belt, separates the oldest Archean rocks of what is known as the Wyoming Province to the north from younger igneous and metamorphic rocks to the south. Attached to the rocks north of the Cheyenne belt are some younger Early Proterozoic metasedimentary rocks similar to those in the Medicine Bow Mountains to the east. The Archean rocks of the Wyoming Province extend northward from the Sierra Madre to form the Precambrian cores of nearly all Wyoming mountain ranges. South of the Cheyenne belt in the Sierra Madre are well-preserved metamorphosed volcanic and sedimentary rocks (including basalt, andesite, and rhyolite flows and tuffaceous rocks, shales, and greywackes), as well as some younger granitic intrusions approximately 1.7 and 1.4 billion years old.

One of the early large-scale mining ventures in Wyoming—the Ferris-Haggarty copper mine in the Grand Encampment mining district—was located in the Sierra Madre. At its peak, the copper mine and smelter operation could process 500 tons of ore per day. The mined ore was transported over the Continental Divide to the copper smelters at Riverside via a 16-mile-long overland tram system, remnants of which can still be seen today, most easily at the Grand Encampment Museum. State Highway 70 from Encampment over the Sierra Madre to Savery and Baggs is a scenic drive, especially in the fall when the extensive stands of aspen trees are turning.

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