With more than 3,000 miles of documented trails, it's an online resource designed for mountain bikers.

MTBProject.com launched last month as an online guidebook for mountain bike trails. The site is a partnership between Boulder-based Adventure Projects and the International Mountain Bicycling Association (IMBA), which is headquartered in Boulder.

Developers modeled the site after MountainProject.com, an online climbing guidebook that was started in 2005 by Nick Wilder and Andy Laakmann.

Since launching the site for climbers - which features 100,000 routes and attracted 2 million unique visitors in 2012 - Wilder said he had always pondered creating similar sites for other sports. Last year, he bought a mountain bike and learned how difficult it was to find useful information online about trails.

'Especially if you're not a local, it's impossible to go somewhere else without finding a bike shop or a guidebook, ' he said. 'It was frustrating to me that I had this great resource for climbing. This could exist for cycling, but it didn't. '

Wilder met with IMBA leaders, who also were interested in mapping trails. So IMBA recruited its members and volunteers to take photos and write about trails to begin building the site's content.

The content on both sites is user-generated, so they act as both online guidebook and social network for climbers and mountain bikers. If someone loses a pair of sunglasses while riding, they can post on the site. Chances are, someone will find and return them.

A mobile version of the site soon will be available where users can download maps and information before heading into remote areas with poor cell service. Rather than carrying an entire guidebook, Wilder said, he puts his phone in his pocket.

The site works best as a supplement to a printed guidebook, he added. It doesn't offer local history like a guidebook, but it does boast multiple authors.

'We're trying to do the right thing by the sport, ' Wilder said, who notes he's only heard from a few disgruntled mountain bikers who don't appreciate the site 'spreading the word ' about 'secret ' trails.

There is no tolerance for users who post illegal or permanently closed trails, Wilder said. Those users' accounts are disabled, and the trail is removed from the database. That's been tricky, Wilder said, because mountain bike culture always has been a little bit rebellious.

IMBA spokesman Mark Eller said the organization is hoping to build a bridge between local trail guides and MTBProject.com, which will become a national trail guide.

'A lot of groups say, 'We already have a trail database,' ' he said. 'There's no reason not to continue to have your local trail guides. What we're hoping to do is convince people to add the same trails to a national database so that no matter where you go, all over the U.S., you can find trails. '