Blow Out

A portion of the Blow Out, which may be the largest vocanic vent in Idaho. It’s so big that the other end of the vent feature isn’t visible more than a mile away.

MIDDLE OF NOWHERE — Few travel here other than geology field trips and Bureau of Land Management employees. Chipmunks, antelope, and red-tailed hawks are the usual residents.

Until the first frost hit two weeks ago, there were still yellow rabbitbrush blossoms lining the road. It’s a mecca for those with wanderlust or wanting to get away from it all.

The backside of Craters of the Moon is full of hidden gems. Reaching most of them often requires a truck with high clearance and sometimes four-wheel drive. Today’s road trip is unusual because it doesn’t. It’s safe and easy to reach in a sedan though there will be spots that require slow driving. Also, heading out just after it has rained is not advisable.

One of the wonders of this day trip is it gives you a clear idea of what the pioneers experienced in their long treks along the Oregon Trail. There are few places left like this where you can truly experience the wind-whistling isolation of the sagebrush desert miles from anyone and anything.

“We now drive this all the time,” said John, one of those BLM employees who patrols the backside of the Craters of the Moon National Monument and Preserve. I ran into him out there and we chatted. I never did catch his last name.

“It’s because of Google Maps,” John said, a tall guy in his 30s. “When you search for Craters of the Moon, Google Maps drops a pin on the backside of Laidlaw Park. People head for the pin instead of the visitor center. Some of them are in cars, take the wrong turn and get stuck.”

Laidlaw Park is that big expanse of sagebrush steppe surrounded by long, thin tongues of lava on the southwest side of Craters. It’s accessible by car if you take the right roads.


The Blow Out is to the west of Laidlaw Park along the car-friendly Carey-Kimama Road. Technically, the Blow Out is the remains of a lava lake that overflowed several times. It’s remarkable for its size: it’s more than a mile long and 100 feet deep, though the vent for the Blow Out is deeper than that at 250 feet deep.

The lava lake filled and emptied several times. Some of the filling events were explosive due to the gas content of the lava. You can see this if you look at the rim of the crater, by the presence of frothy lava sandwiched between more solid basalt.

When the lava lake overflowed, it emptied to the south through a drainage channel that is 100 yards wide and three miles long. All of this activity happened around 116,000 years ago, according to a radiometric age date on the basalt of this vent. That’s about 100,000 years older than the “recent” activity of young volcanism along the Great Rift of Idaho next to the visitor center at Craters of the Moon.

You can see the Blow Out clearly in your choice of internet mapping app by typing in the coordinates of the vent at 43.151453, 113.775266. Don’t skip the drive out just because the overhead imagery is good. Looking at a photo just doesn’t convey the jaw-dropping view of standing on the edge of this crater and not being able to see the whole thing, no matter where you stand on its perimeter.

It’s one of the larger volcanic vents on the Snake River Plain. I’m tempted to say it is the largest vent feature because I can’t think of any vents that are bigger. If you like rubber necking cool Idaho geology, it’s a must-see.


If you have time in your day, swing by Snowdrift Crater in Laidlaw Park on your way home. It’s almost as large as the Blow Out and four-fifths of a mile long. It has one astounding feature that the Blow Out lacks.

As you approach the crater, you can hardly tell you’re at its rim until you’re right on top of it. The slope of the ground going up to the crater is very gradual.

Then suddenly you’re there and looking down 150 feet at the tops of an aspen grove. It’s stunning if you catch when the leaves turn, which is right about now, but still an amazing sight any time of year. Antelope often hide in the trees.

The first time I went out to Snowdrift Crater, there was a steep and precarious trail you could follow into the bottom of the vent. That was about 20 years ago. Since then, someone put up a fence to block it off, probably to keep people from stressing out the antelope that like to hang out in the crater.

If you stick to the main roads, you can reach Snowdrift Crater by car, though that assumes you drive conservatively and don’t head out when the roads are wet.


Stock food and water in your vehicle in case you get stuck. It may be one to two days before someone drives by. Tell someone where you are going and when you plan to be back. That way, someone can look for you if you get stuck and need rescue. Don’t do this drive without a spare tire. Basalt is notorious for cutting holes in the sidewalls of tires.

Stop at the visitor center at Craters of the Moon to get the free Craters of the Moon Travel Map. It’s an old-fashioned paper map that’s detailed and accurate, complete with the Blow Out and Snowdrift Crater clearly marked.

Also at the visitor center, pick-up the geological hand-out by Mel Kunst, et al., with the rather tongue-mangling title of “Geology of the Craters of the Moon 30’ by 60’ Map Area and New Perspectives on Basaltic Volcanism of the Eastern Snake River Plain, Idaho.” It gives a detailed travelogue of geologic features as you drive the backside of Craters.

You can also download it and print it for free at


To get to the blow out, head out to Craters of the Moon. You may want to stop at the visitor center regardless since it’s the last bathroom you’re going to pass for many, many miles.

Drive about 17 1/2 miles west past the entrance to the Craters of the Moon visitor center on Highway. 20.

Keep your eyes sharp after 17 miles for your left turn onto North Laidlaw Park Road. Drive 1.3 miles south and then turn left (east) onto Laidlaw Park Road, but don’t expect to see a road sign anywhere saying that.

Laidlaw Park Road will route you over the Carey lava flow, which is ~12,000 years old. In two miles, you will drop into Paddleford Flat. In another mile, you will come upon the intersection of the Carey-Kimama Road, where you will turn right (south). This turn is very well marked.

Now drive 13 miles south.

Be warned that between 4-6 miles south of your turn-off, the road crosses some basalt that has some blind drops and dips. Slowing down is a really good idea.

At 13.1 miles, take the suddenly appearing turn-off to the left with a small brown sign that says “Blow Out.” Park and sight-see. It’s a good spot for lunch if it isn’t windy out. If it is windy out, eat in your vehicle or there will be silt in your sandwiches.

If you have a high-clearance vehicle, there is a turn-off to the left (east) at 11.6 miles that takes you to the very northern edge of the Blow Out. In a half mile, keep your eyes peeled for a hard-to-spot right turn and take it to the top of the knoll. Now you have to walk 100 yards to the edge of the vent, but it’s worth it. Don’t take this road in a low clearance vehicle.

Please do not be tempted to take I-84 to Rupert as a faster way to get to the Carey-Kimama Road. The road heading north is county maintained between Kimama and Laidlaw Corrals, which is to say, not really maintained at all. Ever drive the Arco-Minidoka Road north of Kings Bowl? Yes, it’s that bad.


To get to Snowdrift Crater from the southern parking area at the Blow Out, drive 7.9 miles south on the Carey-Kimama Road to Laidlaw Corrals. Turn left (east) onto the graded gravel road to Laidlaw Park. This road gradually turns to the north.

The big 800 foot tall butte that now dominates the view out your front windshield is the 425,000 year-old Laidlaw Butte. The Craters of the Moon Travel Map says that there is access to the top of Laidlaw Butte, but I’ve never been up there to verify that.

At 7.2 miles past Laidlaw Corrals, the road will cross the 7,300 Grassy lava flow. At 10.8 miles, you will pass South Park Well and Corrals. At 19.5 miles, the road intersects the Laidlaw Park Road at Piss Ant Butte Junction. Incidentally, Laidlaw Park Road is the road that will take you back out to US Hwy. 20 when you’re done exploring.

Cross Laidlaw Park Road and keep going north. The road will eventually curl around to the right (east). Drive 8.7 miles past the intersection. There will be a turn-off to the left where you can pull off and park. This is the southern lip of Snowdrift Crater. Go before the leaves fall off the trees in the aspen grove.

Snowdrift crater has a radiometric age date of 480,000 years, making it one of the oldest features at Craters. The lava that laps up onto the north slope of Snowdrift Crater is 6,500 year-old Little Park lava flow, one of the youngest on the plain.

To get to Snowdrift Crater directly without visiting the Blow Out, just go straight on Laidlaw Park Road instead of turning onto the Carey-Kimama Road. It is 11.2 miles to Piss Ant Butte Junction from the intersection of the Laidlaw Park and Carey-Kimama Roads.