Monterey, Calif. » As a relatively new convert to mountain biking, I'm already familiar with the hazards of this pastime.

In my short two or three years as an enthusiast, I've been a victim of protruding roots, tire-swallowing sand pits, teeth-jarring washboard trails and slick, half-buried rocks that have sabotaged my good times like rain on a picnic.

But I never thought I would have to worry about Claymore mines, hand grenades, 3-inch antitank rifle grenades and 81-millimeter mortars.

These and other military explosives are potential -- although rare -- hazards on the hiking and biking trails of the Fort Ord Public Lands, a 7,200-acre recreational area about 10 miles east of Monterey.

Before it closed in 1994, Fort Ord was one of the nation's largest military training facilities, preparing soldiers for the two world wars, as well as Korea and Vietnam. The Bureau of Land Management took over a portion of the old military base in 1996 and threw open the gates to more than 80 miles of hiking and mountain-biking trails.

There was one hitch: The Army had yet to find and remove every last piece of ordnance from the scenic, oak-studded rolling hills. We are talking about rockets, mortars, mines, grenades and other weapons of demolition.

Fast forward to me, in early February, mounting a hardtail bike (no rear suspension) at a trail head on the western border of the old military base. As I prepared for a day of riding, I pulled a safety-warning pamphlet out of a box marked "trail maps" and scanned the photos of World War II- and Vietnam War-era weapons.

"If you find an object that resembles those shown in the photograph -- don't touch it," the pamphlet said.

No kidding.

And I used to worry about running into protruding boulders, ocotillo plants and rabid pit bulls.

But in two days of riding at Fort Ord, I encountered no antipersonnel weapons. I rode like a madman over the emerald hills, etched in a spider-web network of single-track trails, fire roads and paved streets. And, yes, I had a real blast.

It's no wonder that the Fort Ord Public Lands hosts the annual Sea Otter Classic (April 16-19 this year), a biking competition and festival that draws more than 50,000 athletes and fans from around the world.

On both days of my visit, I started with a muscle-burning grind up steep hills blanketed in green grass, chaparral and brush oak. Once at the summit, I had to stop to admire the views of gently rolling hills stretching to the sea to the west and dropping toward the fertile fields of the Salinas Valley to the east. Moss hung on the craggy oak trees like tinsel on a Christmas tree. Overhead, turkey vultures and red-tailed hawks cut figure eights in the partly cloudy sky.

The real fun began at the top. I swooped down the smooth, hard-packed dirt trails, over whoop-de-dos that lifted me off the bike pedals, then dropped me hard on my seat. The trails curved left and right like a slithering snake, around oak trees and shrubs. Blind curves were as common as chaparral. I flirted with disaster but escaped riding headlong into another biker or hiker. Because the park has more than 80 miles of roads and trails, the chances of colliding with another visitor are relatively low.

I left hoping this was the start of a new American trend: Shuttered military bases are converted to hiking and mountain-biking playgrounds.

Make fun, not war.