Hells Half Acre

Hikes: D, O.
Total Distance, D: 2-11 miles.
Difficulty: Levels I, III.
Season: March 1-December 1.
USGS Map: Kettle Butte SW, Morgans Pasture NW.
BLM 100K Map: Circular Butte.
Dirt Road Miles: 1/4 good dirt.
PLSS Location: Section 22, T2N R34E.

Introduction: Hells Half Acre is a 66,000 acre lava flow that has been recommended for wilderness by the BLM. Just 20 miles from Idaho Falls, it is a real plus for that town. The flow is from 3400 to 4100 years old, and has accumulated enough soil to allow junipers, grasses, and ferns in shaded cracks. It is almost all pahoehoe, which makes for excellent hiking, and as a bonus it includes several large lava lakes. And, its trailhead is on a paved highway, for virtually year around access. What a great place for a person's first hike on lava!

The Hike: You can hike to the spectacular vent, 4 1/2 air miles in, or you can just goof off near the trailhead. The author recommends that you not attempt the vent on your first hike here. Take one warm up hike to get familiar with pahoehoe hiking, and to learn how the trailhead area looks. This lava flow doesn't like to give up its secrets too quickly, so try the vent on your second or third hike.
  This shouldn't restrict you too much: on his first outing here, the author spent two hours wandering about and taking pictures, and then only 15 minutes getting back to the trailhead... Hiking near the trailhead is rated Level I. Hiking to the vent is rated Level III because of the area's remoteness, because of a short aa stretch, and because of the constant routefinding.
  To start, climb the edge of the flow from the trailhead. Move a bit to your right (to the west) along the first ridge. There are four main environments on this flow. First are the ridges and rough areas, such as you are on now. Second are the lava lakes, relatively level areas with some very flat platy surfaces that make fast going. Third is a mix of the first two. Fourth is the aa and rubble near the vent.
  Pure ridges or pure lakes offer the fastest going. When you are on a mix, you must constantly make decisions. Inevitably, among the hundreds of choices you make, a few will be wrong. When you goof, and you confront a crack that looks too big to comfortably cross, just relax and don't try anything dangerous. There is almost always a safe alternate nearby--and if there isn't, just backtrack. Don't try to jump across cracks. Especially, don't try to jump down: this is very hard on the knees. Instead, try to take a long stride across the crack, using your regular walking rhythm.
  That's about all you need to know to explore near the trailhead. Finding your way back should be easy: your car is parked just to the west of the farthest north (closest to the highway) part of the flow. If you come out on the west side of the flow, just follow the flow's edge until you come to the trailhead. If you see yourself coming out too far east, bear west.
  Your route to the vent is easy. Almost any time you are on a ridge, you can see the vent: the low, dark, rather wide butte almost due south of the trailhead (labeled "Neck" on the USGS map). There are an infinite number of routes to the vent. That's the glory of lava hiking: no two people follow the same path. And, your maps are almost worthless. The ten foot contour interval they use is too small: there are too many contour lines to really help. The author wonders if 20 foot contours wouldn't be more useful.
  However, two main lines seemed to make sense to the author. He approached the vent by walking south from the trailhead across a large lake; continuing south across a ridge area; and then walking south across another lake. When that wore out, there was a bit of mixed hiking, followed by a few short stretches of aa close to the vent. This last stretch was about the most fun of all. (And after all that talk about the maps, you can kind of see this route on the map if you look hard enough--and if you've been there!)
  The vent is one of Idaho's great wonders. The map doesn't even give a clue to its majesty. If you day hike, reserve at least an hour to poke around the vent. If you can overnight hike, you'll have even more time here.
  Once on the vent, you can pick a return route. The author went just a bit east of north, and was able to avoid all the aa. He then continued to the trailhead along a route that stayed east of the two lava lakes. This was excellent for a long time, but later got bogged down in a lot of mixed terrain. The best route is probably to leave the vent as described, and then cut northwest for a while until you hit the lava lakes.

Access: Start in Idaho Falls, at the intersection of Broadway and Skyline. Drive 20 1/4 miles west on US-20, and turn left on a dirt road. There is a BLM sign which misspells "pahoehoe". Turn left at a junction which comes quickly, and then left again to reach the parking area.