Volcanoes and related igneous flows are a staple of the Pacific Northwest landscape, so it is interesting to observe that Idaho’s highest mountain range presents a 60 mile front of sedimentary limestone.
How did these Lost River mountains align the way they did, and how did they reach their current height? Much can be explained by the movements of the North American tectonic plate over the last 11 million years, when compression and extension forces initially faulted the surface crust. Also, two glaciations over the past 100,000 years left their mark. But a far more powerful source, arising from deep within the earth, are the volcanoes. Their presence can be seen along much of the backside of the Lost River Range. The largest igneous flow begins at the mouth of Pass Creek, continues north then northwest, to form a large apron around the range. The keen observer, with a little imagination, can trace the roots of long gone Mesozoic stratovolcanoes on the order of Rainier and Orizaba. The limestone which piled up against their eruptive flanks gave the birth to our Lost River mountains. Three stratovolcano locations, tentatively identified are: Arco Valley (between King Mtn & Arco Hills), Wet Creek Basin, and Upper Pahsimeroi.
Here’s a look at some remnant Lost River volcanic peaks. Clockwise from top left.
VULCAN PEAK 10297′ The highest volcanic summit in LRR. View S to USGS Peak, 1999.
APRON MOUNTAIN 9382′ View NE to Hawley Mtn & Lemhi Range, showing Wet Creek stratovolcano caldera, 2007.
EAST BURNT PEAK 10149′ A prehistoric cairn? View SW to Cleft Peak, 1999.
THE CAPE 8387′ Iron rich andesite of Eocene Challis Volcanics. View S to Massacre Mtn, 2007.
GROUSE PEAK 8464′ The northernmost Pahsimeroi/LRR summit overlooks the Round Valley caldera. A TM Bannon 1914 triangulation station, 1994.
VICTORIAS SECRET 8860~ Beauty is in the eye of the beholder, 2007.
SQUAWTIP 9046′ The most prominent topographic feature in the Burnt Creek area. A conical peak of rugged andesite breccia. There is no easy line to the summit. First ascent Lee Morrison, Lester Walker, USGS, 1934-5.
SQUAWTIP The easiest way up Squawtit is a zig zag climb on its east face & gully system. The average slope angle is 65 degrees, 2007.
CAMPION PEAK 9597′ A 2005 cairn and view SW to Borah Peak. Campion is a pink alpine flower.
SPRING HILL MOUNTAIN 9449′ A 1932 benchmark placed by EM Buckingham. View to Doublespring Pk, 1996.
DRABA HILL 9315′ Above Horseheaven Pass. Draba is a bright yellow circumpolar flower abundant in this area, 2005.
BABY PEAK 9191′ Heads Baby Creek in lonely cowboy country, 2005.
Any errors of opinion or observation in this article are mine alone…….Rick Baugher, May 2007
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