The Lost River Range stretches 70 miles from northwest to southeast between Challis and Arco. The Big Lost River Valley and Salmon River flank the range on the west, and the Little Lost and Pahsimeroi rivers are along its east side. The range contains not only the highest point in Idaho, 12,662-foot Borah Peak, but also seven of the state’s nine 12ers, the 12,000-foot peaks. The Range is covered in the book from pages 265 to 295.
Idaho’s Lost River Range is an actively uplifting fault-block at the northern end of the Basin and Range province. Extensional faulting has lifted the range relative to the down-dropped Big Lost River basin on its west side, producing steep ridges and slopes essentially devoid of foothills. Interior and eastern regions of the range are deeply incised by the Pahsimeroi and Little Lost Rivers. Most of the range, particularly in the central and southern regions, consists of thick layers of Paleozoic limestone and dolomite. Multiple episodes of tectonic deformation have resulted in dramatic open to isoclinal folding at a scale of meters to kilometers. Glaciation has carved numerous cirques throughout the range and alpine lake basins are scattered in the central and eastern portions. These combined activities have created an impressive assortment of large, high angled faces with western, northern, and eastern aspects.
Pat McGrane’s article covering his 2007 traverse from Borah to No Regret Peak is an excellent read, The High Route to No Regret Peak, as is Wes Collins’ 2014 account of his Borah to Lost River Peak, The Lost River Traverse.
If you are interested in Ski Mountaineering in the range check out Cody Feuz’s Hi-Adventure website.