Big Southern Butte

Elevation: 7,550 ft
Prominence: 2,390

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Big Southern Butte is the highest and largest volcanic cone in the Snake River Plain. At 300,000 years old and 7,550 feet in height, it is also one of the youngest and largest rhyolitic volcanic domes. This is one of Idaho’s most impressive mountains. Driving past it on US-26, it often mysteriously appears to float just above the Snake River Plain and looks larger than life. Driving towards it across the desert, it seems to grow larger with each mile. Driving or hiking up the access road will impress upon you the scale of the geological forces that created the butte and the surrounding plain. USGS Big Southern Butte

Big Southern Butte viewed from the west.

Big Southern Butte as viewed from the west.

The access road was originally built to access a fire lookout on the summit. The lookout was last manned in 2004 and was removed sometime after that. The BLM still maintains the road probably because of electronic installations at the summit. The BLM closes the road during the winter. Many people hike the road from the gate. It is 1,800 vertical feet and 3.5 miles from the gate to the summit. Sheldon Blustein’s page on this Butte is the definitive resource for this butte. Check the BLM’s web page for current condition


Access is complicated because a large section of the land north of the butte is part of the Idaho National Laboratory and is closed to the public. Google Maps gives directions across the INL land with a proviso that access is compromised. Do not follow this route. I have provided two access routes below. There are undoubtedly other options from the south and southeast but I have not explored them.

BLM Directions

The BLM gives the following directions which, in my opinion, are probably accurate but too vague to follow.

From Arco: Take the County Road/300 North heading south (this is signed as the ‘Arco OHV Route’). Turn east onto Arco-Minidoka Road/2930 North. Turn onto 2900 West heading south and turn west onto 2150 North. Turn north onto 300 West, which turns into 2225 North. Turn onto the Arco-Minidoka Road heading south for several miles. Turn east onto Quaking Asp-Frenchman Road toward Big Southern Butte. At Frenchman’s Cabin, turn and head up the Butte.

Western Approach (My Driving Route)

From the junction of US-26/US-93, drive west out of Arco on US-93 for 2.0 miles. Turn left/south onto the paved (and signed) 3100W road and zero out your odometer. After I turned off US-93, I tried Google Maps again and this time the App gave me directions for the following the western approach route something it would not do when I was in Arco.

Follow 3100W south for 4.5 miles, crossing a cattle guard at 4.2 miles. Keep left when the road splits. At 13.9 miles, take another left fork. The road deteriorates after this point. At 17.6 miles, take the left fork. At 20.6 miles, you will cross a cattle guard and, at 23.9 miles, you will reach the Frenchman Cabin. At this point, you have crossed nearly 24.0 dusty miles with many protruding rocks. I recommend that you only access the area during dry conditions in a high-clearance vehicle with all-terrain tires.

From the cabin area, a road heads directly toward the butte. The road was recently graded in July 2018.  At 26.9 miles, there is a hang glider warning sign and, at 28.7 miles, you will reach the summit. There is a large turnaround where the lookout once stood. This final stretch of road is steep, very rocky in places and exposed in many spots. A 4WD is recommended.

Looking west from the summit showing the middle section of the access road.

Looking west from the summit, showing the middle section of the access road.

Looking east from near the hang glider takeoff spot.

Looking east from near the hang glider takeoff spot.

The middle section of the access road viewed from the summit.

The middle section of the access road as viewed from the summit.

The Twin Buttes are two more impressive volcanic features located east of Big Southern Butte.

The Twin Buttes are two more impressive volcanic features located east of Big Southern Butte.


Mountain Range: Snake River Plain

Year Climbed: 2018

Longitude: -113.0233   Latitude: 43.39601

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