You’re driving through the High Sierra, probably headed toward Mammoth Lakes or Yosemite, and you see a sign for Devils Postpile National Monument. It sounds like one of those roadside oddities, right? Like a "world’s largest ball of twine" situation but with rocks. Honestly, most people just breeze past it because they’re chasing the big-name granite walls of El Capitan.
That’s a mistake.
The place is weird. It’s a geological freak show that looks like someone took thousands of giant, hexagonal pencils and shoved them into the earth with a sledgehammer. But there is a lot of nuance to visiting this place that most travel blogs gloss over. It isn't just about the rocks; it's about a bizarre cooling process that happened 80,000 years ago and a waterfall that makes most people's Instagram feeds look like a lie.
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The Science of These Hexagonal Pillars
Geologists have been arguing about this place for a while. For a long time, the consensus was that the Postpile was about 100,000 years old. Newer potassium-argon dating suggests it’s actually closer to 82,000 years. That sounds like a small distinction, but in the world of volcanic history, it’s a big jump.
Basically, a lava flow hit a natural dam—likely a glacial moraine—and pooled up. It was deep. We’re talking 400 feet deep. Because the lava was trapped in a big "lake," it cooled incredibly slowly and evenly. As basalt cools, it shrinks. If it shrinks at a perfectly uniform rate, it cracks into these hexagonal columns.
Nature loves hexagons. Look at honeycombs or dragonfly eyes. It's the most efficient way to pack shapes together without leaving any gaps. At Devils Postpile National Monument, you’re seeing that efficiency on a massive, terrifying scale. Some of these columns are 60 feet high. They are so straight they look man-made.
Then the glaciers came.
About 20,000 years ago, a massive glacier slid over the top of these columns. It acted like a giant belt sander. If you hike to the top of the Postpile—which you absolutely should—you can see the "pavers." It looks like a polished tile floor. You can actually see the "glacial polish" and striations where the ice dragged rocks across the basalt, scarring it forever. It's slippery when wet, so don't be that person who wears flip-flops on a granite hike.
Getting There is a Whole Process
You can't just drive up to the monument whenever you want. During the peak summer months, the National Park Service runs a mandatory shuttle from the Mammoth Mountain Main Lodge. It’s a bit of a hassle. You have to pay a fee, wait in line, and sit on a bus with twenty other sweaty hikers.
But there’s a reason for it.
The road down into the Reds Meadow Valley is narrow. It’s basically a paved goat path with steep drop-offs. If everyone drove their own SUVs down there, the whole place would be a permanent gridlock of people trying to back up on blind curves.
Pro tip: If you arrive before 7:00 AM or after 7:00 PM, you can usually drive yourself. Also, if you’re staying at the Reds Meadow Resort or one of the campgrounds, you get a pass. Being down there in the valley when the shuttle isn't running feels like you’ve found a secret world. The light hits the Minarets—those jagged peaks in the distance—and everything turns a weird shade of purple.
Rainbow Falls: The Better Half of the Trip
Most people walk the 0.4 miles to the Postpile, take a selfie, and leave. That’s a bush-league move. If you’ve already made it to Devils Postpile National Monument, you have to keep walking another 2.5 miles to Rainbow Falls.
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The San Joaquin River drops 101 feet over a cliff of volcanic rock. Because of the way the mist kicks up, if the sun is at the right angle (usually mid-day), you get a permanent circular rainbow at the base of the falls. It’s loud. It’s misty. It’s significantly more impressive than the rock columns if we’re being totally honest.
There’s a lower falls too, about another half-mile down. Hardly anyone goes there. If you want a spot where you can actually hear your own thoughts, keep walking past the main overlook. The trail is dusty, though. Pumice soil is basically powdered glass and ash, so your shoes will be gray by the time you're done.
The 1992 Earthquake and Why it Matters
People think these rocks are permanent. They aren't. In 1992, a series of earthquakes rocked the Mammoth area. A bunch of the columns at the Postpile actually snapped off and tumbled into the talus pile at the bottom.
When you look at the base of the monument, you see a massive heap of broken segments. It looks like a giant’s toy box was tipped over. It’s a reminder that this whole formation is incredibly fragile. You aren't allowed to climb on the columns themselves, and for good reason—gravity is eventually going to win. The monument is essentially a slow-motion collapse.
Why the Name?
The name "Devils Postpile" is a bit of a 19th-century trope. Back then, if explorers found something weird or slightly intimidating in the wilderness, they slapped "Devil" on it. Devils Tower, Devils Garden, Devils Punchbowl.
In 1911, it was almost destroyed. A mining company wanted to build a dam that would have blasted the columns into rubble to create a rock-fill wall. Thankfully, John Muir and some early conservationists pressured President William Howard Taft to use the Antiquities Act. Taft signed the proclamation, and the "Postpile" was saved. It’s one of the few times early 20th-century bureaucracy actually did something cool for hikers.
Wildlife and Safety Realities
This isn't a theme park. It’s high-altitude wilderness. You’re at about 7,500 feet. If you’re coming from sea level, that 5-mile round trip to the falls is going to feel like a marathon. Drink twice as much water as you think you need.
There are black bears here. Lots of them. They aren't the "eat your face" kind of bears, but they are the "destroy your car for a Snickers bar" kind of bears. If you’re camping, use the lockers. If you’re day-hiking, don't leave a cooler in your backseat. The rangers here are strict about this because a "food-conditioned" bear usually ends up being a dead bear.
Also, watch out for the wind. The "Windthrow" area near the monument shows the aftermath of a 2011 windstorm where gusts hit 100+ mph. Thousands of trees were snapped like toothpicks. It changed the landscape overnight. Nature in the Sierras doesn't do things halfway.
Practical Steps for Your Visit
If you're actually going to do this, don't just wing it. The season is short—usually mid-June to October, depending on how much snow the Sierras got over the winter. Some years, the road doesn't open until July because there's still twenty feet of snow blocking the pass.
- Check the Reds Meadow Shuttle schedule before you leave Mammoth. If you miss the last bus, you’re walking a long, uphill way back to your car.
- Pack a lunch. There is a small store at Reds Meadow Resort near the end of the road, but their hours are erratic and they might run out of the good sandwiches by 2 PM.
- Wear real socks. The pumice dust is brutal. If you wear those tiny no-show socks, the grit will get in and give you blisters before you even hit the waterfall.
- Go to the top of the columns. Most people just look from the bottom. The "floor" made of hexagonal tiles at the top is the most unique part of the monument.
- Hit the Soda Springs. Near the Postpile, there’s a carbonated cold spring. The water literally bubbles out of the ground. It tastes like pennies because of the mineral content, but it’s a trip to see "sparkling water" in the middle of a meadow.
Devils Postpile National Monument represents a very specific moment in Earth's history where everything aligned—the lava chemistry, the cooling rate, and the later glacial carving. It’s a fleeting structure in geological terms. Go see it before more of it ends up in the rock pile at the bottom.
Actionable Insights:
- Best Time to Photograph: Arrive at Rainbow Falls between 11:30 AM and 1:00 PM for the best rainbow visibility.
- Avoid the Crowds: Take the first shuttle of the morning (usually around 7:15 AM) to have the Postpile to yourself for at least thirty minutes.
- Permit Info: You don't need a special hiking permit for the day use areas, but if you plan to head into the Ansel Adams Wilderness from here, you’ll need to snag a wilderness permit via Recreation.gov months in advance.