Angel Island State Park, San Francisco Bay: Paved and dirt roads on this mostly undeveloped, 470-acre island offer panoramas of the Golden Gate Bridge, the bay and more — if the day is clear. If not, enjoy the quiet and stop by the historic 1910 U.S. Immigration Station, which processed nearly 1 million newcomers. Info: (415) 435-5390, http://www.parks.ca.gov/default.asp?page_id=468.
Blue Diamond, Nev.: Outside Las Vegas, about six miles southeast of Red Rock Canyon, tiny Blue Diamond is the gateway to a variety of trails, good for novice and expert cyclists alike, in rugged desert foothills and canyons. Whichever you choose, bring lots of water, slap on sunscreen and beware of sand traps — on the trail, not the golf course. Info: McGhie's Bike Outpost, (702) 875-4820, http://www.mcghies.com.
Downieville, Calif.: Daring mountain bikers delight in Downieville, at the foot of the Sierra Buttes about 100 miles northeast of Sacramento, where old gold mining paths have been turned into bike trails. Not for the inexperienced. Some single tracks, studded with sharp rocks, wind down thousands of feet past sheer drops. Info: (800) 200-4949, http://www.sierracountychamber.com.
Haleakala volcano, Hawaii: Whooshing down the twisting pavement from the 10,023-foot Maui mountain to the sea is one of the biggest thrills in road cycling. But it's not without risk. After a string of fatalities, Haleakala National Park in 2007 imposed a moratorium on commercial downhill rides. Individual cyclists can still make the trip. Info: (808) 572-4400, http://www.nps.gov/hale.
Los Angeles to San Diego: The ultimate beach ride, this 140-mile journey is fairly flat, save an infamous hill in San Diego County. Although you'll encounter traffic, you'll often be on bike paths, residential streets or at least a road shoulder — rare for a coastal trip. Info: Adventure Cycling Assn., (800) 721-8719, http://www.adventurecycling.org. Its Pacific Coast Route Section 5 map costs $11.75 for members, $14.75 for nonmembers.
Mammoth Mountain Bike Park, Calif.: With more than 70 miles of trails in the Sierra, this bike park at a top ski resort scores with newbies and experienced cyclists alike. Ride the Panorama Gondola to McCoy Station or the 11,053-foot summit and pick a path down. Polish your skills on dirt jumps and other challenges at Kamikaze Park. Info: (800) 626-6684, http://www.mammothmountain.com.
Moab, Utah: The legendary Slickrock loop, which bounces and twists for 10 miles along a sandstone plateau above the Colorado River, is just one of many trails near this small town that test expert riders. The thrills and breathtaking vistas — if you dare look — are worth it, despite the crowds. Info: (800) 635-6622, http://www.discovermoab.com.
Palo Camado and Cheeseboro canyons, Calif.: Trails and fire roads that traverse these areas, near Agoura Hills in the Santa Monica Mountains National Recreation Area, take in a diverse landscape — grassy hills, oak groves, chaparral and creek beds — and wildlife such as hawks. Info: (805) 370-2301, http://www.nps.gov/samo.
San Luis Obispo to Avila Beach, Calif.: On this 12-mile Central California trip, you'll start out on city streets and a frontage road along U.S. 101, amble down a tree-canopied creekside path and finish at a gorgeous bay. Info: San Luis Obispo County Bicycle Coalition, (805) 547-2055, http://www.slobikelane.org.
Ventura to Ojai, Calif.: This 16-mile route, on two very different bike paths, transports you from the sea to the mountains. The funky Ventura River Trail threads through an industrial district dotted with public art and ends at a shady park. The Ojai Valley Trail then climbs into tree-studded hills, affording killer views. Info: http://www.cityofventura.net/visitors (click on "Ventura River Trail Guide" under "Maps"); http://www.traillink.com/trail/ojai-valley-trail.aspx.