EUGENE, Ore. (AP) — Donnie Kolb has been organizing gravel bicycle rides for the past five years.

Usually keeping his events a bit on the down low — Kolb’s outings are unsupported, unsanctioned, have no entry fee and crown no winner — the Portland lawyer typically sees about 100 riders show up for his “bikepacking” adventures after posting the GPS coordinates of the route and a “We’re doing this on Saturday morning” message on his website, VeloDirt.com. Last year, his Dalles Mountain 60, a 60-mile single-day ride on gravel and dirt roads on both the Washington and Oregon sides of the Columbia River near The Dalles, attracted about 200 cyclists, most yet for a VeloDirt ride.

“The longer they are,” Kolb says about his rides, “fewer people show up.”

So when Kolb posted his newest and boldest route, what he has dubbed “The Oregon Outback” — a 360-mile gravel epic that starts in Klamath Falls in far Southern Oregon and ends at Oregon’s northern border, the Columbia River — he figured he would have a hard time getting 50 other adventurous souls to ride the path he and photographer Gabriel Amadeus blazed last summer.

To his amazement, he had to shut down registration after 400 bikers emailed Kolb that they could not get their cycling kits on fast enough to join him.

Welcome to the next big thing in biking.

Gravel grinders, dirt road touring, bikepacking — call it whatever you want — interest is sky-high across the state in rides that eschew the pavement and explore Oregon’s abundance of dirt and gravel roads. Whether on road, mountain or cyclocross bikes, cyclists are flocking to these often off-the-radar group rides that are all about self-sufficiency, exploration and visual beauty — and usually involve a lot of climbing.

“People have been road riding forever,” says Nastassja “Staj” Pace, the destination development coordinator for Travel Oregon, the state’s official tourism agency. “This is a way for people to go back to their childhood when you’d hop on your bike and take off down whatever kind of road.”

Travel Oregon has taken notice of rides like Kolb’s and races such as the Oregon Coast Gravel Epic in Waldport popping up on the state’s cycling event calendar. (Locally, Bend bike/beer/coffee hangout Crow’s Feet Commons is organizing a Klamath Falls-to-Bend multiday event along the Oregon Outback trail the second week of May.) The state already promotes Oregon’s various mountain bike trails, popular road routes and designated scenic bikeways, and gravel rides could be next. According to Pace, a 15-person working committee on scenic gravel rides has already been formed, and select routes could be highlighted on the state’s bike-specific tourism website, RideOregonRide.com, in the next year.

“There’s not a lot of ego and people are just out to have fun,” says Bend’s Rob Angelo, who competed in the Oregon Gravel Epic last year, about the emergence of gravel riding. “It appeals to both road riders and mountain bikers. Any time you can … make a marriage between those two groups and pull in a cross section of the biking community, you’re going to have something pretty popular.”

“People are really interested in getting into the beautiful backcountry Oregon has to offer,” adds Pace, who spoke about gravel grinders recently in Eugene at the first Oregon Bicycle Adventure Summit. “These are pretty intense adventures. You’re really getting away from it all.”

Gravel rides are not for the casual cyclist or spin class all-star. Kolb’s Oregon Stampede ride is a single-day, 127-mile loop near the small rural towns of Dufur and Moro near the Columbia River, a route that features 9,000 feet of climbing. The Oregon Outback ride not only rolls on for 360 miles but includes at least one 70-mile stretch along which no drinking water is available. The Oregon Coast Gravel Epic named its long ride “The Abomination” when race organizer Steve Cash told his riding partner — after 10,000 feet of elevation gain over 73 miles — “This is either a great ride or an abomination.”

Says Kolb: “You need to be pretty self-sufficient. You need to be able to fix a flat, use a GPS (unit), read a map. You could be on a road that only sees two cars a day, and if you break down, there’s a good chance those cars have already gone by. It’s that kind of riding.”

Of course, that remoteness is part of the appeal.

“Oregon has all these amazing areas,” says Kolb, who has bike toured on- and off-road throughout the West and Alaska. “Places that even cars don’t go on. A lot of these gravel roads — they aren’t marked — you just have to look at your map and your GPS and make your best informed guess. But that’s why I love it.”

In this June 7, 2013 photo, Donnie Kolb pushes his bike through a marshy section of Sycan Marsh near Klamath Falls, Ore. Kolb has been organizing gravel bicycle rides for the past five years, usually keeping his events a bit on the down low. His outings are unsupported, unsanctioned, have no entry fee and crown no winner. (AP Photo/The Bulletin, Gabriel Amadeus)