Twentymile Lava Trail is a 9.6 mile moderately trafficked out and back trail located near Idaho Falls, Idaho that features beautiful wild flowers and is rated as moderate. The trail is primarily used for hiking, walking, and trail running and is best used from March until October. Dogs are also able to use this trail.

Distance: 9.6 miles Elevation Gain: 367 feet Route Type: Out & Back

dog friendly

hiking

walking

running

wild flowers

rocky

A 0.9-mile loop or a 4.5-mile trail to the main vent of the flow. Both are unimproved and marked with poles. Hiking in lava fields is unique because of the rough terrain, unusual scenery, and the contorted landscape. Since this is a Wilderness Study Area (WSA), permanent trails have not been developed. The unimproved hiking routes are marked with poles. Blue top poles mark a route around a short loop which is a good introduction to lava hiking. The 0.9-mile loop takes about 30 minutes to walk. On this loop note the pressure ridges, deep cracks with ferns at the bottom, and moss on rocks. Red top poles mark a 4.5-mile route to the main vent or source of Hell's Half Acre lava flow. This is a strenuous hike and a round-trip to the vent can take a full day. Water is essential and boots with good soles are advisable. Estimated time to hike to the vent is 2-3.5 hours (one way).

hiking
5 days ago

Part of this trail had a fence closed and you couldn’t go through. But I made a great loop to go around two or three times.

hiking
no shade
rocky
scramble
19 days ago

We went on a hike here on a Sunday afternoon and it wasn’t real busy. There is essentially no shade and the trail is kind of hard to follow. They have these big stakes with a blue or red ribbon on them that is supposed to mark the two different trails but we only saw blue markers. I would not recommend bringing a dog. There are a lot of cracks in the Lava and small cactus on the ground that are sometimes hidden.

hiking
no shade
rocky
scramble
1 month ago

This trail was actually pretty busy. Probably people just trying to get a hike in during quarantine. It cleared up after you get beyond the blue poles. Good hiking boots and water are a must, a trekking pole is a big help. I would not recommend this trail for dogs, the lava rock is sharp and can heat up quickly. Also there are cacti tucked into the rocks and along hidden under the sage brush. The hike takes longer then you’d expect because you need to spot your next pole then figure out how to get there over broken terrain, crevasses and shifting rock. It is a good early hike since it tends to be dry and clear of snow long before other trails are passable.

hiking
no shade
off trail
rocky
scramble
1 month ago

We just hiked the loop trail, which was about a mile. It was fun! We went earlier around 10:00 AM, and there wasn't a lot of people there.

hiking
1 month ago

This is a great one and done experience. The blue trail often has a group or two of people, but the red trail is pretty secluded. This is definitely not a good trail for pets and kids. There will be many crevasses and lava tubes to hop over, which would be pretty stressful with younger kids. Spring and fall are best. There is no shade at any point unless you want to crawl into a lava tube or hide under some shrubbery. The full trail, with one short 10min break, took about 7.5 hrs due to the uneven terrain and taking time to locate trail markers. This is good for a single hike, but I’m not sure I would hike it again unless this type of geology is your thing.

hiking
no shade
off trail
1 month ago

rocky
6 months ago

I am the geologist for the BLM which manages this trail. It is a very rugged trail with a lot of elevation up and down. I would add that the blue loop trail is 0.45 to the beginning of the red trail to the vent. That is another 4.5 miles so the total is 10 miles and longer than the 4.5 each way. Plan ahead. November was a perfect time. Cool beautiful. No snow and not too hot. Highly recommend. The silence and solitude was amazing!!

11 months ago

Fun afternoon. As noted, there really isn't a trail aside from moving from one post to another. The trail posts are marked blue for the loop and red for the way to the vent. We didn't make it all the way to the vent today due to a storm rolling in. The cactus were close to blooming, give it another week and it will be gorgeous.

hiking
11 months ago

This is a 10 plus mile hike .... very little elevation but with the ground so uneven it takes longer then you might think . So be prepared ... no cover remember lots of water and sunscreen ...

hiking
Thu May 16 2019

We went last week taking the shorter blue post loop. We followed the trail clockwise (from a top down with north as 12 o’clock) had trouble near the end of the loop finding the last few posts, so we back tracked. There was a small storm that blew in mid day with a little hail. It’s pretty wide open so if it’s a windy day in town, it’s hella windy here. Don’t bring your dog unless they are used to wearing boots, and you are comfortable watching to make sure they don’t lose one.

hiking
no shade
rocky
Sun May 12 2019

Start early. Bring plenty of water since there is none available. There is almost no shadow, so bring a sun protection with you. This will test your path finding skills, because you have to follow poles - no actual trail on the ground to follow. Sometimes the poles are difficult to spot - the heading is about 170 when you get to the red marked poles. Also wear heavier boots, you will be hiking ona sharp lava rock. Consider trekking poles for more stability. Saw a rattlesnake and a marmot.

Sun Mar 24 2019

Only done the short trail. Area is scenic but the trail is a little difficult to follow.

Fri Mar 22 2019

If you want an adventure of having to find the trail, this is the place. Just make sure that there is absolutely no snow when you go. There was still a few snow patches when I went and they could be hiding a crevasse underneath, and you wouldn't want to walk over that. but a fun trail none the less :)

hiking
Wed Mar 20 2019

A wonderful hike for late May - the cacti are blooming, so you see pink, orange and white flowers right on the lava rock!

Sat Nov 17 2018

Definitely worth coming during a setset. I can see how some people might find it boring during the day, but the sunsets are worth the hike/trail run. There's not really a trail, but it's definitely doable if you're willing to Boulder a little bit.

hiking
Thu Jun 28 2018

Pets not recommended unless they've spent plenty of time walking in shoes already. Definitely make sure they are a good fit too! We've gone out with our dog, but turned back because his shoes kept coming off. Lava rock is not ok on bare dog paws, its sharp and gets hot. Set your dog up to have a good time outside. If its windy in Idaho Falls, its windy A.F. out here. The scene out here is pretty awesome if you haven't grown up here and haven't seen lava fields before.

Thu Jun 14 2018

Take plenty of water. The lava rocks reflect a lot of heat and you will need it. I would never take my dog out there!!! Rough trail and sharp rocks. Always pack a flashlight just in case and understand that it is impossible to follow the poles in the dark and the trail is not like a dirt trail that's easy to follow. I did a search and rescue mission out there. It's real easy to twist an ankle and get lost. That's my 2 cents.

hiking
Sat Apr 21 2018

It’s a nice hike and decent workout, but somewhat bland scenery. The patterns of the lava flow are interesting, but create a rugged terrain. I wouldn’t recommend it for dogs, there’s several sharp rocks and small cacti hidden between them. A few families were there with small children (under 10yrs) who seemed to be struggling because of the large crevasses and loose uphill rocks.

hiking
Fri Apr 20 2018

Cool hike but do not take dogs onto any volcanic rock lightly. People only! Dogs will need booties. Also, it can get windy out here, windy enough that any hats need to be physically strapped on and jackets need to be zipped or they can catch gusts that will knock you off your feet.

Wed Sep 13 2017

Great hike and some very odd scenery but the trail said it was pet friendly and my Great Dane' s paws would definitely disagree

Fri Jul 14 2017

Poles are hard to follow for the trail. Very rocky and dry. Bring water and shoes you don't mind getting trashed. Big volcano crater at the end which is pretty cool.

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