City of Boulder Open Space and Mountain Parks has maps of all the trails in their domain -- which is a lot of them. Check out which ones are OK for bikes at bouldercolorado.gov/openspace . You'll also find tons of info on mountain biking in Boulder County and beyond at bouldermountainbike.org .
E ver take that mountain bike off any sweet jumps?
Save some of that jumping for the Valmont Bike Park.
But bike-park P.S.A.: Make sure you're riding the right type of bike for the jumps, and within your ability. Also, don't talk to strangers.
Valmont has cool little loops of singletrack with nifty features to ride, or not (there's always a bailout). But if you're looking for miles of trail -- and an occasional sweet jump off a rock or over a log -- go for the miles of trails beyond the bike park.
Bikes aren't welcome on all of Boulder's trails, so snag a map from a local bike shop or check out the trail maps on the county's Open Space website or Boulder Mountainbike Alliance's site to make sure you're in the know before you head out.
Also, be a good trail steward. Don't ride when it's muddy and tear up the trail. Fortunately, it's not hard to find dry trail around here most of the year.
1 Marshall Mesa
Location: Just south of Boulder
For your first taste of mountain biking in Boulder, head to Marshall Mesa for some mellow, rolling trail on wide-open plains -- or connect to trails beneath the Flatirons.The trails close to the trailhead, like Marshall Valley, are the mellowest. Head south and west, across Colo. 93, to check out the connecting trails, like the High Plains and the Spring Brook loops.
If you've never mountain biked, this is a great place to start.
Trailhead: Take Colo. 93 south of town. The trailhead is on the southeast corner of 93 and Marshall Road, across from the Eldorado Corner Market.
2 Hall Ranch
Difficulty: Moderate to advanced
Location: Southwest of Lyons
The trails at Hall Ranch offer some of the area's best dirt riding -- big climbs, sweeping singletrack and a grand vista of Longs Peak.
To avoid the rock garden on the Bitterbrush Trail, start toward the Nelson Loop via the Antelope Trail. It has all the climbing (and switchbacks), but fewer bigger boulders to pop over or hike-a-bike.
When you get the chance, speed with joy along Nelson's hardpack, enjoy the big views and enjoy the long ride back down the hill.
Trailhead: From Lyons, head north out of town on U.S. 36. Turn left on Apple Valley Road, then left on Antelope Drive, which ends at the trailhead. Parking at trails in and near Lyons can be tricky, so carpool and be courteous with where you park (OK, so there was another PSA. But this one's important for access).
3 Picture Rock
Location: South of Lyons
Since the Picture Rock Trail links the trails at Heil Valley Ranch to Colo. 7 near Lyons, you can link Heil to Hall for a monster MTB ride.
To reach Heil's loops -- Ponderosa, 2.6 miles, and Wild Turkey, 2.9 miles -- head up through wide-open spaces to tight, rocky turns through foothills forest.
If you bike to Hall, take a snack, because it's a fair amount of riding.
Trailhead: Take Colo. 7 south out of Lyons to Old St. Vrain Road. Turn left, then left again on Red Gulch Road.
4 Walker Ranch
Difficulty: Moderate, advanced if you ride the hike-a-bike
Location: West of Boulder
For days when you're looking for a high-mountain feel without actually driving to the high country, Walker Ranch has that vibe -- plus plenty of climbing and technical sections to make you bust out your MTB mojo. But it's not far out of town. Yay Boulder.
Recommendation: Ride the loop clockwise, and unless you're a pro, hike-a-bike the stairs. Bonus climbing points if you ride up to the trailhead from Chautauqua -- this is known as "Super Walker."
Trailhead: Take Baseline Road west; past Chautauqua, it turns into Flagstaff Mountain Road. Make a left at the signs for Walker Ranch, just after Pika Road.
Location: North of Nederland
For some at-altitude gnar, the Sourdough Trail (and other trails it leads to) can provide solid adventure riding. Be ready for tight switchbacks, baby heads and rock gardens, all through the thick forest beneath the Indian Peaks.
To seek out more of the goods, pick up the Little Raven Trail on the south side of the Red Rock Trailhead, or take the Sourdough north from there to pick up the South St. Vrain Trail.
Trailhead: To reach the Red Rock Trailhead, head toward the Brainard Lake Recreation Area, off of the Peak to Peak Highway just northeast of Ward. The trailhead is just shy of the entrance station for the recreation area.