In the middle of summer in the high desert of Nevada and on the alpine slopes of California’s Sierra Nevada, the trails were so dusty I was breathing in dirt. Some sections of the trail had deteriorated so badly it felt like I was riding my bike through sand on a beach. One day, I was rolling through switchbacks on a graded descent. All was going well—I was riding fast and building momentum with the trail—until my front tire ran smack into a patch of moon dust, dirt so fine it sucked all the energy out of my front tire. My bike bucked and I landed, hard, on my back. A cloud of dust hung in the air around me.
We needed rain. The trails needed to soak up a bit of moisture, to transform the moon dust into its opposite, hero dirt. This kind of dirt does not steal your momentum. It gives it back to you in abundance. It’s smooth and creates traction, which boosts confidence and speed. Because it’s so often found after a storm, and because it’s as fleeting as untracked snow, and because mountain bikers so often compare the sport to skiing, hero dirt is often called brown pow.
It’s well known that mountain biking is the closest thing to skiing in the summer—riding fast down a flow trail in moss-covered woods generates the same momentum, the same adrenaline, the same giddiness as skiing through those woods when they are covered in snow. Like powder, the best dirt often occurs right after a storm. And when conditions line up, riders rearrange their priorities and clear their schedules to take advantage of smooth, grippy, tacky dirt.
What is Brown Pow?
Some places are blessed with better dirt than others—it depends on the climate, how covered the trail is, the natural filtration and draining systems in the forest and the soil. More than a type of dirt, and whether it’s clay or sand or silt, brown pow is a feeling. It’s the smell of rain in the forest and the calm that comes when drops accumulate on green leaves. It’s relief that the rocks and the dust have settled and the trail is resetting after a long period of wear. It’s the sensation of riding as fast as you can in the absolute best conditions on your home turf.
Looking for brown-pow aficionados, I found a mountain bike group based in Oregon called the Disciples of Dirt. Their 140-plus members are stewards of trails in the Southern Willamette Valley, a 150-mile-long stretch of fertile land in Oregon that’s known for great pinot noir. The same dirt that grows such temperamental grapes is also really good for mountain biking.
Brown pow is “really nice brown clay soil that’s just smooth. It provides a ton of traction,” said Jeff Green, a lifelong Eugene resident who is on the board for Disciples of Dirt as secretary. “We’ve had some rainfall, which allows for ultimate traction, but yet it’s not muddy. Personally, I think that September and October are two of the best months for mountain biking in Oregon.”
Dry. Tacky. Mud. There is a fine line between the phases of dirt on a trail, said Green, and it makes all the difference in your riding. The sweet spot, as always, is in the middle.
Too dry and the trails accumulate a layer of loose dust that rubs between the bike tire and the trail, which reduces friction, said Green. It doesn’t have to be a thick layer—it might almost be invisible—but it still reduces the traction when you ride around sharp corners.
Too much rain, and the trail becomes muddy, which isn’t good either. According to IMBA, mountain biking on muddy trails is a faux pas. Riding your bike through mud leaves trenches in the trail. Not only does this wreck the trails, it’s disrespectful to the volunteers who spent hours building them. Even if you live below the snow line, you shouldn’t assume the trails are suitable for year-round riding.
“If they don’t handle moisture well, we tend to stay off of them because they get muddy and sloppy and it wrecks the trails,” said Green. “When it’s extremely wet, that’s not going to provide that much traction, either. Especially when you combine that with roots and rocks that also have a lot of moisture.”
Sometimes you can find brown pow in the spring, but often the trails are so saturated with snowmelt that they become muddy. The fall tends to be just right. Of course, this varies from region to region. Some spots, like in the Southwest, have great riding year-round and are known more for their smooth rock. But in forests that sprawl across the continental United States, just a little bit of moisture and the dust packs back down on the trail. There’s no fine, extra layer between the tire and the compacted soil. This is what Green calls hero dirt.
“Especially with flow trails,” said Green. “You’re able to go around corners so fast you feel like you’re invincible. You’re able to apply a lot of pressure, take turns sharply and quickly and not worry about your tires pushing out from underneath you.”
How to Find It
After a long spell of high pressure, when your bike shoes are so dusty you can hardly touch them without getting dirty, the day you see a storm brewing in the forecast is a good day. Then, you just have to wait for the rain and hope it’s enough. Where I live, at the beginning of the fall, after a rainstorm, the best dirt is usually found up high, where the air is cooler and the storms are stronger. But as the season inches closer to winter, the snow steers riders to lower and lower elevations to hunt for brown pow.
In the Sierra Nevada, where I live, the rain came at the end of September. At first it didn’t rain enough—just a drizzle for a couple of hours—and the sun came out. But then temperatures dropped and it rained more and more. The rain lowered the temperatures significantly and brought a dusting of snow to the highest peaks. In other parts of the West, the storms were so cold they dropped inches of snow, not rain, skipping fall altogether. But in lower-elevation destinations, like the trails Green and the Disciples of Dirt ride, conditions lined up to be the best of the year.
A few days after the rain, I started pedaling down a flow trail that descended more than 4,000 feet from a fire lookout to the valley floor. It was cold at the top, colder than I expected, and I pulled out my wind-stop layer—an essential piece of gear for fall mountain biking. After a summer of riding on loose, silty, unstable dust, it took me awhile to adjust to the compacted dirt. I rode my brakes harder than I should have. I was hesitant and scared. But gradually, I got a feel for the trail’s loops and twisting turns. I eased up on my brakes and leaned into my bike to apply pressure on the trail. It didn’t catch my front tire. On the contrary, it built upon my momentum and sent me flying down the mountain. It felt, almost, like I was skiing.