I've always been a little compulsive when it comes to planning vacations. By Jan. 15 I can tell you that on the morning of Aug. 2 my family and I will be in the Haunted Mansion at Disney World. Or en route to Denver in Row 17 on United Airlines Flight 369. Or at the Museum of Modern Art in New York if it rains, but Ellis Island if it doesn't.

My passion for planning is entirely sound -- travel surprises are almost never happy ones.

Or so I thought. After a week hiking alone in the desert and canyon country of southern Utah, I now know that some kinds of travel are dominated by the unexpected, and that it's the serendipitous moments that make these trips memorable, indeed worthwhile. Four experiences stood out -- three of them wonderful and one terrifying. All were unanticipated.

Desert Storm The wind is rising. For anyone with enough sense to get out of the rain, now is the time to seek shelter. A lash of lightning flickers over Wilson Mesa, scorching the brush, splitting a pine tree.

-- Edward Abbey,

"Desert Solitaire"

Abbey, the late writer, naturalist and desert enthusiast, was writing from Utah's Arches National Park, and he gives a pretty good description of what I see there early one morning in October as I hike north on Devils Garden Trail. Of course I don't turn back when I spot a storm approaching; I've been planning months for this hike, which will bring me to some of the most beautiful natural stone arches in the world. And, anyway, everyone knows it hardly ever rains in the desert, especially in the morning.

But everyone is wrong. By the time it's clear that I'm going to get soaked, and maybe zapped by lightning, I'm two miles from my car. But near Double O Arch I find a rock ledge overhanging an area just big enough to keep me and my camera gear dry. As I sit down on a rock to await the passing of the now-torrential rain, a chipmunk scurries in my direction. I guess that I'm occupying his shelter.

Indeed, the little animal stops just short of the overhang, stares at me for a moment in what I take to be rank indignation, then runs to the lee of a rock some yards away. To make amends, I throw him a few raisins and nuts from my trail mix, then turn my attention to the storm.

Jagged blue bolts of electricity shoot continuously from purple clouds, striking the red buttes and mesas around me. The wind whistles and reverses direction inexplicably, and water begins to flow in a nearby dry wash. By the time the hardest rainfall comes, sunlight has already reappeared from the east, turning the tracks of rain into dazzling needles of gold. It is a thrilling show, one I will not forget.

Now the rain has nearly stopped, so I rise to resume my hike. Already I can smell the marvelous smoky-sweet scent the desert creosote bush emits when it's wet. I look for my friend the chipmunk, but he's gone.

And so is the trail mix I tossed to him, so now I don't feel guilty.

Sound of Silence I stopped to swab the sweat from my face. The silence locked around me again like a sphere of glass.

-- "Desert Solitaire"

Just after sunrise, it's not yet hot enough to make me sweat as I make my way along the White Rim Trail in Canyonlands National Park. I will soon stand on the edge of a mesa 1,200 feet above a sandstone bench called the White Rim, and some 2,200 feet above the gorge where the Colorado and Green rivers meet to form Cataract Canyon.

There I will gaze at one of the most incredible and inaccessible places in the United States, a fantastic jumble of multicolored canyons, mesas, spires and fins stretching as far as the eye can see.

But first I stop to photograph something on a smaller scale, the silver-gray skeleton of a juniper tree silhouetted against the cobalt sky. As I compose the picture I am struck -- almost literally -- by the silence. It is an utter absence of sound -- no wind, no birds, no airplanes, nothing. There is just a faint ringing in my ears. Background noise from the brain's neurons?

I realize that I have never before experienced total silence. It is at once magnificent and unsettling. I think about this as I resume my hike: Why should I find this experience both pleasurable and troubling? It is pleasing, I think, because the lack of stimulus is calming, like floating in warm water. And troubling, perhaps, because it is evocative of death.

In a few moments I stop again to sample the sound of silence, but now a slight breeze has sprung up and the spell is broken.

Like the chipmunk, the silence is gone.

Slickrock I can see V-shaped black wings in the lonely sky, soaring higher and higher against a yellow sunset. I think of the dead man under the Juniper tree on the edge of the world, seeing him as the vulture would have seen him, far below and from a great distance.

-- "Desert Solitaire"

At the end of the much-used Devils Garden Trail in Arches National Park lies an alternate return route, the so-called Primitive Trail through Fin Canyon. The route is well named. Indeed, the National Park Service has posted a sign there warning of "difficult hiking."

But how difficult can it be, I wonder? Haven't I just survived a thunderstorm unscathed? The "trail" is little more than a sequence of cairns -- little stacks of red sandstones that park rangers placed at intervals as markers. For a few hundred yards I proceed without much difficulty along a dry wash that descends into the canyon. Periodically the wash makes a vertical plunge of 10 to 20 feet down a dry waterfall. At these, I find my route by following the cairns.

But at one such point the only cairn in sight is at the very bottom of a waterfall, some 20 feet straight down. It's not clear how I'm supposed to reach it. I start across a bare rock surface that skirts the cliff edge at the right and slopes toward it. I have been hiking all morning across these steep "slickrock" surfaces with no problem. With good hiking shoes, they really are not slick.

Unless they are wet. Halfway across, I fall suddenly and slide toward the drop-off. I grab at some low-lying juniper branches, but the tree is long dead and the branches break away. My slide stops for a moment, and I'm left lying on my right side facing forward.

No problem, I think, I'll just roll over onto my other side and carefully work my way back the way I came. But every time I try to roll over, I slide a little closer to the edge.

I'm struck by the idea that I could die here, and soon. My immediate thought is for my family. How could I do this to my wife and two daughters? I feel sick to my stomach, the physical side of fear.

I dig my toes and fingers as best I can into little rock crevices and ridges and slowly inch my body forward toward safety. I am now just a few feet from the precipice, but I don't slide farther toward it. On safe ground at last, I find a long, circuitous route back to Devils Garden Trail.

I consider taking a picture of the "difficult hiking" sign, but decide against it.

Discovery All is curved and rounded, the course of the main stream and canyon as indirect as a sidewinder, winding upon itself like the intestines of a giant.

-- "Desert Solitaire"

Abbey was hiking the canyon cut by the Escalante River, but he just as well could be describing Utah's slot canyons, those extremely narrow but deep slices in the earth cut by the abrasive material in flash floods over the millennia. For years I've wanted to photograph the innards of a slot canyon, which can be stunningly beautiful as their sinuous sandstone walls reflect the sunlight in red, pink and gold tones.

Also, I admit to a certain fascination with the dangers of exploring these places. Periodically one reads of hikers in a narrow slot being swept away to their deaths by a flash flood, hit by a roaring freight train of water, mud and debris spawned by unseen thunderstorms miles away.

My plans to explore the Little Wild Horse slot canyon near Goblin Valley State Park are thwarted twice. Thunderheads are boiling up on the horizon the first time I approach it. Going into a slot canyon in the face of a storm is out of the question, and indeed an hour later it rains hard.

Next morning, with not a cloud in sight, I return to the five-mile dirt road that leads to the canyon. It's immediately clear I can't negotiate the road in the slippery mud left from yesterday's rain. Nature photographers have a joke: What's the difference between a rental car and a four-wheel-drive vehicle? Answer: The rental car will go anywhere. Funny, but not true.

But I have one more chance to explore and photograph a slot canyon -- the Peek-a-Boo Canyon in Grand Staircase-Escalante National Monument, where I am headed next. I'm warned by a ranger there that the canyon has a lot of water in it from recent rains and I should be prepared for waist-deep or even neck-deep wading.

After bumping along for an hour on the dirt Hole-in-the-Rock Road and hiking a mile down a steep incline, I arrive at last at Peek-a-Boo's upper entrance. But I don't go in. The opening looks like a sinister, crooked smile carved in the earth. It's so narrow I'll have to remove my backpack to squeeze in.

Slot canyons are narrow by definition, but this one is too narrow, too dark, too muddy, too scary for someone with mild claustrophobia. Besides, I haven't forgotten my recent experience on wet slickrock.

Discouraged, I turn around for the long hike out of Coyote Gulch, which Peek-a-Boo empties into. Maybe I'll try again next year.

But what is this? Isn't this another slot canyon right in front of me, one that's a comfortable 10 feet wide at the entrance? It is, I learn later, the Dry Fork of Coyote Gulch, and it's just a little too wide to properly be called a slot canyon. None of my guidebooks even mentions it.

I am able to penetrate this near-slot canyon several hundred yards before it gets too water-filled to go on. I spend more than an hour in there, happily taking pictures and enjoying the serpentine passages illuminated by reflected sunlight.

Aided by several hundred photographs, there's a lot I'll remember from my trip through southern Utah. But it's the little unexpected things -- mostly not recorded on film -- that are likely to stay with me the longest. And it's the promise of more serendipity that will lure me back to the desert.

For the desert "wears a veil of mystery," Abbey writes. "Motionless and silent, it evokes in us an elusive hint of something unknown, unknowable, about to be revealed."

How could I ever plan for that?

Gary H. Anthes, an editor at Computerworld newspaper, welcomes the chance to escape technology whenever he can.

Unexpected Utah sights: the narrow Dry Fork of Coyote Gulch, left, at Grand Staircase-Escalante National Monument, and a juniper tree at Canyonlands National Park. Along the White Rim Trail in Utah's Canyonlands National Park, hikers can experience utter silence -- no planes, no cell phones, not even a chipmunk.In Utah's Arches National Park, hikers can scramble along rough trails or simply find an overlook and gape at the vista.