Drafting effortlessly at 20 miles an hour up Marsh Creek Road, the approach to California's Mount Diablo is anything but devilish. San Francisco lies unseen 50 miles to the west, but the northwest flank we're rolling up is a terraced valley of picturesque farmland. And then the road curves and Diablo's profile changes. The mini peloton breaks up. I'm forced to stand on my pedals to climb. Just as the summit's observatory comes into view, the road narrows to one lane and increases its pitch to a leg-searing 16 percent on the final ascent. It's a challenge fit for the pros: The 2012 Tour of California raced up Mount Diablo on May 15 for the first time in race history. Slovakia's Peter Sagan won the 115.3-mile stage in 4:50.49 Time. We're riding 50 miles of the course two weeks before the stage.

Diablo is a unique peak, and not just for California roadies. From the 3,848-foot summit, one can see more of the Earth's curvature and farther into the distance than from any other point on the planet, except the 19,000-foot summit of Africa's Mount Kilimanjaro. That's thanks to local geography: Mount Diablo is the highest point around, rising steeply from sea level.

We are wrapped in clouds on the summit, but a clear day reveals views 54 miles south to Mount Hamilton, east to the Sierra, and down to the Golden Gate Bridge. We race down the banked switchbacks at 40 miles per hour, exiting the state park and turning towards Morgan Territory Road. The road is well maintained and nicely banked, making for fast, smooth descents. Though there is still 2,500 feet of climbing to go, the reward is a descent along sweeping, perfectly timed curves for miles. The road is so narrow that it feels like a 30 mph singletrack carved through a tunnel of trees. We blaze past a string of food marts, believing we're close to home, but then mile 50 ticks over on the cyclometer. Out of food and water with another 40 miles still in front of us, I consider saying "aaahh" to catch the passing bugs for a little extra protein. We finally find the Marsh Creek intersection and turn for the final 13 miles back, bonked but still spinning. —Sydney Fox

If you go: Ride a 63-mile loop (3,400 elevation gain) from Marsh Creek Road through Clayton, up Mount Diablo via North Gate Road and down on South Gate Road, through Danville up to Morgan Territory Road and back to Marsh Creek. Step up to the Tour of California route; details here. Park at local shopping centers, or pay the fee to leave a car in Mount Diablo State Park. Get a local's take at Clayton Bicycle Center and Encina Bicyle Center (encinabicyclecenters.com).