Elevation: 7,550 ft
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.
The access road was originally built to access a fire lookout on the summit. The lookout was last manned in 2004 and 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 feet and 3.5 miles from the gate to the summit.
Access is complicated because a large section of land north of butte is part of the Idaho National Labratory and closed to the public. Google Maps gives directions acrossed the INL 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 Country 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 Approcah (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 cattleguard 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 take the left fork. At 20.6 miles you will cross a cattel 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 conditons and with a high clearance vehicle with AT 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 waring sign, and at 28.7 miles you will reach the summit. Where there is a large turn around where the lookout once stood. This final stretch of road is really steep, very rocky in places and exposed in many spots. 4WD recommended.
USGS Big Southern Butte.
Regions: SNAKE RIVER PLAIN
Mountain Range: Snake River Plain
Year Climbed: 2018
Longitude: -113.0233 Latitude: 43.39601