[img:614680:alignleft:medium:Big Sister from Little Sister]
Big Sister peak lies almost dead-center between Diamond Peak and Bell Mountain in the Lemhi range of eastern Idaho. And shares a ridgeline with Little Sister, which (who?) sits just over a mile away to the west.
The Lemhi range is the eastern-most range completely within Idaho. This is classic basin-and-range, with flat valleys separating some serious uplifting. The rock found in the Lemhis varies according to the strata, with volcanic rock interspersed with limestone uplifts and folding.
Big Sister is officially known as Peak 10894. Rick Baugher, an accomplished local climber and mountain historian, stated that on his summit visitation on September 22, 1990, he did not see any sign of prior summit visits. Baugher claims first ascents for many of the peaks in eastern Idaho, and on his first ascent of this one, he named this one in honor of his oldest daughter, calling it Lexi’s Peak. In a similar fashion he named it’s smaller adjacent summit for his younger daughter. Possibly influenced by Baugher, the official bible of Idaho climbing Idaho, A Climbing Guide by Tom Lopez, refers to these two peaks as Big Sister and Little Sister
Be careful with fire and leave no trace.
And don't eat the cow pies.
[img:614682:alignright:medium:Mud Springs campsite from the West Ridge route]
The “trailhead” at Mud Spring makes a great site for car camping. Alternately, there is a more civilized campground on the other side of the valley off Wet Creek Road, or at the head of the Little Lost Valley to the north you will find Barney Hot Springs, which might offer some camping.
Or if you're looking for something softer, there are motels in Arco and more in Rexburg or Pocatello.
There may be several ways to climb Big Sister. For the most popular route (if you can call it that; in most years Big Sister probably does not get climbed), follow the West Ridge route for Little Sister. It may also be possible to climb Big Sister from the east via Rocky Canyon, but the map indicates a long, long approach and steep climb. If you try it, please write a report.
From the top of Little Sister, head westerly on the connecting ridgeline. This ridge entails a 600’ elevation loss, then an 800’ elevation gain. It’s Class 2, but somewhat steep. The distance from Little Sister to Big Sister is about 1.25 miles.
The easiest descent route is to retrace your steps. By the time you have climbed Big Sister (and Little Sister twice) you will have logged about 8.5 miles and 5100’ vertical gain. It’s a big day.
If you go early enough, you may find snow to climb, easing the difficulties presented by all that talus.