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.
Getting ThereHigh clearance required. 4WD recommended.
These directions start at the tiny hamlet of Howe, Idaho. Howe has a grade school, a Mormon church, and if you are lucky there is a gas station and café that are sometimes open. Don’t count on them being open, but the café has a reputation for offering great food.
To get to Howe from the west, follow Highway 22/33 from Arco. Or from the south or east, follow Highway 26 from Pocatello or Highway 33 from Rexburg.
Once you get to Howe, take the only road north, the Little Lost River Road, also known as Summit Creek Rd. In about 30 miles you'll come to the even smaller hamlet of Clyde, demarcated by a single BLM building.
About 100 yards past Clyde, a small stream passes under the road. Immediately after, there is a rough 4wd road. Go another 70 yards and take a right on a good gravel road (which is soon joined by the 4wd road, but you might as well take advantage of what seems like an improvement in eastern Idaho).
The gravel road immediately crosses the Little Lost River to a T intersection. Turn right onto a rough 4WD, high-clearance road that runs between the river and the hillside for a little ways before coming out onto a flat sagebrush plain. After a few up-and-downs over perhaps a half mile, take a sharp left at a wooden post (no sign, but the road obviously heads uphill toward the brush of Cedar Run Creek). At a Y intersection, stay left, again heading for the brush of the creek.
The road follows the creek, crossing it twice in steep in/out transitions requiring high clearance and possibly 4wd. Also, the upper road is quite rocky in places.
A word of caution: On the way there, you can become very distracted by the sight of Bell Mountain. Keep it between the lines.
Be careful with fire and leave no trace.
And don't eat the cow pies.
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.
RoutesThere 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.
External LinksMackay info
Splattski trip report
Lost River Ranger District, Salmon-Challis National Forest
Lone Pine cam, on the other (east) side of the range at 6300'
For additional information on this climb and other peaks in the area, please see Tom Lopez's excellent book, Idaho: A Climbing Guide.