Hell's Half Acre
Brochure | Map
Hell's Half Acre Lava Trail traverses the desert ecosystem of the Snake River Plain through rough terrain, unusual scenery, and contorted landscapes created from multiple lava flows. Most of the calderas left behind by the violent eruptions of the Yellowstone hotspot have been buried by many less violent, Hawaii-type lava flows associated with the stretching of the Basin and Range. The most recent flow in eastern Idaho is the Hell's Half Acre lava flow which erupted about 4,100 years ago and is 125 square miles. The lava that flowed in these basaltic eruptions was probably about 2,000 degrees Fahrenheit, the consistency of molasses, and traveling at speeds up to 30 mph.
Hell’s Half Acre is designated as a National Natural Landmark (NNL) and a Wilderness Study Area (WSA). These designations help preserve the area so the public can enjoy and study this unique geologic area in its healthy, natural condition. The Lava Trail System is open to non-motorized recreation activities only.
A Closer Look at the Lava Landscape
Hiking across the lava is a unique experience. Lava rock is extremely sharp, glassy and fragmented, with open cracks, lava tubes and caves. The most prevalent landscape consists of A'a (ah-ah) and Pahoehoe (pa-hoy-hoy) lava flows. Pahoehoe lava is more fluid than A'a. It's outer surface cooled faster than the interior causing a "ropey" appearance. The less fluid A'a formed leaving rough, irregular mounds. The areas of soil and vegetation not covered by lava area called "kipuka," a hawaiian word meaning 'window in the lava.'
Read about Hell's Half Acre geology
Botany
A variety of plants and wildflowers contrast the black and gray lava flows. In the spring and early summer, numberous wildflowers, such as Evening Primrose, Indian Paintbrush, wild onions, penstemon, geraniums, and Prickly Pear Cactus, color the landscape. Also coloring the landscape, are ferns growing in deep cracks and a variety of desert vegetation. The spectrum ranges from tiny mosses and lichens to juniper trees hundreds of years old. Other native species include sagebrush, rabbitbrush, bitterbrush, blue bunch wheatgrass, and needle-and-thread grass.
Wildlife
Wildlife roaming the lava flows include mule deer, antelope, sage grouse, bobcats, coyotes, foxes, and occasional snakes. Soaring above the flows are red-tailed hawks, prairie falcons, and golden eagles.
Visitors can explore Hell's Half Acre in three different locations:
| Area | Description | Directions |
1.) Hell's Half Acre Trail (Northbound) | Two developed lava trails with interpretive signs discussing geology and biology of the lava flow; Popular destination for environmental education groups. | Located about 20 miles southwest of Idaho Falls and 5 miles east of Blackfood. While traveling northbound or southbound on Interstate 15, take the "Blackfoot Rest Area" exit. The interpretive trails are close to the parking area. |
| 2.) Hell's Half Acre Trail (Southbound) | Two developed lava trails with interpretive signs discussing geology and biology of the lava flow; Popular destination for environmental education groups. | Located about 20 miles southwest of Idaho Falls and 5 miles east of Blackfoot. While traveling northbound or southbound on Interstate 15, take the "Blackfoot Rest Area" exit. |
| 3.) Twenty Mile Trail | Undeveloped trails offering scenic solitude; Short 0.5 mile loop trail and a 4.5-mile trail to the main vent, or source, of the Hell's Half Acre flow. Both trails are unimproved and marked with poles | From Idaho Falls, travel west on Highway 20 until reaching mile marker 287. Continue 0.3 miles until reaching a sign noting "Lava Trail." Turn south onto the gravel road and continue one-quarter mile to the trailhead. |
Fees/Facilities:
- Shelter
- Fire ring
- Portable toilet
- Unimproved parking
- Use season- all year (usually spring, summer, fall)
- Length: Main Vent Loop- 4.5 miles; Lava Flow Loop- 0.5 miles
- Hiking level: Easy-moderate
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