The Redwood stage is heading on over the hills

They're the world's tallest trees and wide enough to drive a car through. No wonder Dom Joly couldn't wait to go into the woods

I wasn't exactly nervous about visiting San Francisco, just a touch hesitant. I have no personal problem with that lot's deviant lifestyle. What they get up to in their own time is their own business. It is apparently considered perfectly normal to see them out and about in everyday social situations. Nevertheless it still came as a bit of a shock when I saw my first hippy.

I wasn't exactly nervous about visiting San Francisco, just a touch hesitant. I have no personal problem with that lot's deviant lifestyle. What they get up to in their own time is their own business. It is apparently considered perfectly normal to see them out and about in everyday social situations. Nevertheless it still came as a bit of a shock when I saw my first hippy.

San Francisco is a city of sub-cultures and it positively thrives on them. One of the most prominent of these groups are the cybergeeks. I often wondered what happened to all the four-eyed computer nerds that used to hang around in corduroy groups at school swapping Dungeons and Dragons tips. Now I know: they all went west to work in Silicon Valley for companies such as Apple, Netscape and Yahoo! and pour into the city at night to spend their cyberbucks.

The weird thing is that, although they all still wear exactly the same kind of spoddy outfits that they did at school, they somehow now look really cool. They are certainly a lot richer than I am and I looked ridiculous in my trendy London Carhartt togs. Back in the UK they're fairly expensive and respectably hip, but over here Carhartt is what proper workmen wear and I looked like a slightly plump mechanic. I'm sure the geeks were laughing at me. Just in case, I stood up and punched a couple of them for old times' sake before running to my Chevy Impala and heading for the Golden Gate Bridge to start my road trip up north.

It's quite embarrassing to admit that the original kernel of an idea for this journey came from Jonathan King, the aesthetically challenged self-publicist recently released from a spell indoors at Her Majesty's Pleasure. Way back in the Eighties, he presented a show called Entertainment USA, in which he would gurn his way round America telling us how brilliant he was. In one episode he was in Northern California in redwood country and I became transfixed by these extraordinary giants - the tallest trees in the world, growing up to 370 feet, and often wide enough to drive a car through their trunks. They grow in a raggedy line starting around San Francisco then running north along the coastline before petering out just over the border in Oregon. I always knew that I'd go and see them one day, but it was a recent article in The New Yorker about a man who climbs these monsters that made me embark on my short, tree-based, solo, mid-life-crisis road trip.

I started my journey by driving a short way up Highway One, indisputably the most beautiful road in the world. It hugs the rugged Pacific coastline from San Francisco to just after Fort Bragg before turning inland, unable to traverse the almost impenetrable "Lost Coast", the wilderness home to some of California's most privacy-obsessed individuals. I passed by Muir Woods, the closest place for day-trippers to play dwarf in the redwoods' giant act, but I had been warned that these were mere matchsticks compared to those further north, so I kept on trucking.

Highway One is stunning and every hairpin turn brings another breathtaking view of sheer cliffs and wind-mangled trees on the coastal side, while almost-neolithic, lush, green hills rise up on your right, occasionally ceding their superiority to enormous forests of eucalyptus and black oaks. Hitchcock shot a lot of films here, including The Birds and Vertigo, and you can see why. The menacing coastline plus the fierce clouds and driving rain are gloriously sinister.

I was up for some luxury before totally disappearing into the unknown, so I turned off Highway One and headed inland towards Napa Valley, the capital of California's wine and food fixation. I got there by crossing the Sonoma Valley which locals had told me was far more beautiful than its famous neighbour. They weren't wrong. The valley is an unspoilt little piece of the south of France right in the middle of the US and I took my time negotiating a tiny road over verdant hills into Napa itself.

Napa is a long flat valley saturated in vineyards or "wineries" as they are known here. At the northern end of the valley, an extinct volcano called St Helena looms large and forbidding over the endless miles of vines basking in the valley's peculiar micro-climate. I spent the night in an extraordinary b&b on top of the only hill in the middle of the valley. After a hard day's wine-tasting at some of my favourite wineries, Venge and Quintessa, I took full advantage of the hot tub perched on a high slope overlooking the entire valley. I found it difficult to drag myself off for some grub despite the preponderance of amazing restaurants, including the French Laundry, in the nearby towns.

The next day, I made my way slowly back west towards the coast, stopping in the sweet little town of Ukiah to ogle the local beers at a micro-brewery before driving down the glorious Anderson Valley, passing through the town of Boonville, the inhabitants of which have invented their own language for communication between themselves when the rare stranger appears in town. It's not the most difficult language: outsiders are known as "headlights", because that is often how they are first spotted in the valley. But I felt that there were probably quite a lot of "samenames" about, or "kissing cousins" as we know them, so I moved on sharpish.

The last 10 miles to the coast took me into my first proper redwood forest and I wasn't disappointed. The road snaked through the shadows of the surrounding titans and I felt a strong urge to park the car, leave my clothes in a neat pile and lose myself in the forest. I quickly changed my mind and drove on, tuning into some right-wing nuttery on the local talk-radio stations for light relief.

Driving in the US is pretty easy. Almost every car has a sticker on it indicating which way the occupants voted in the election. The rules are simple. If the car ahead of you has a Bush/Cheney sticker, approach with caution, don't overtake, and let them do what they want because they are certainly heavily armed rednecks willing to make you "squeal like a pig" at the drop of a plaid baseball cap. If, however, the hydrogen-fuelled vehicle in front of you sports a Kerry/Edwards sticker then put your foot down, run them off the road, steal their hub-caps, whatever: they'll blame it on your underprivileged upbringing and forgive you.

Back on Highway One, I turned north and headed towards Fort Bragg, my destination for the night. Just before I reached it, I drove through the town of Mendocino, perched perilously on razor-sharp cliffs above a raging Pacific. It's a picture-postcard kind of town, crammed full of arty types - every other wooden building is an art gallery or an arts and crafts store. Ten minutes later, I arrived in the slightly more blue-collar Fort Bragg, slap bang in the middle of a whale festival.

Every year, on that particular weekend, hundreds of whales hang out in the bay taking a break from their long migration to the Arctic to laugh at coach-loads of whale-watchers. I'd never met a whale-watcher before, but it quickly became clear that they mix in the same social circles as "twitchers" and stamp collectors. I imagined that many had children working happily in Silicon Valley and decided to take a rain-check on entertainment. I stayed in my room at the Grey Whale Inn, which used to be the town hospital. My room was once the delivery room. It is apparently traditional for anyone in the town born in the room to come back and spend their 50th birthday night there. Fortunately, I slept alone.

I left Fort Bragg the next morning and meandered along the remainder of the coastal stretch of Highway One. As I turned inland towards my final destination, the town of Eureka, I caught a panoramic view of the "lost coast", an extraordinary concept in surf-obsessed California. Seafront property is still available, but bring a shotgun and a big digger.

A couple of hours later, I was deep into Humboldt County, weed capital of America, and beards had suddenly become compulsory. I turned off Highway One just before Eureka and took a far more scenic approach through the Avenue of the Giants. This is a 30-mile drive through a forest of absolutely enormous redwoods. If only I'd had a convertible, I could have gazed up into the veritable cathedral of trees that briefly became my only sky.

I drove through a couple of shifty-looking towns that were clearly heavily reliant on the weed industry. It didn't need Sherlock Holmes to work this out because the only stores in town were for hydroponic lights, fertiliser and, weirdly, spa baths. At least our bearded friends washed occasionally, even if they weren't that keen on organising tastings for eager tourists. This was no Napa Valley.

I arrived in Eureka, a large, fairly unexciting town to find an unlikely oasis in the form of my hotel for the night, the Carter House Inn. It possessed the single longest wine list I have ever come across and I took full advantage of it. I also had a seven-course meal that ranks as one of the best of my life.

The next day, I trooped around the pretty historical centre of Eureka in about 10 minutes before visiting the neighbouring town of Arcata. This is what Humboldt County is all about. The town has a green council which has offered "legal sanctuary" to any US serviceman who doesn't fancy fighting in Iraq and the earth flag flies proudly in the middle of the lovely central square. I imagine the Freak Brothers retired here. There's a large university, too, so the place is lively and everyone looks a bit like Ben and Jerry. It was a gorgeously mellow place to end my North Californian adventure.

Driving back south, I visited a couple more enormous redwood forests and visited the town where Bigfoot was first spotted, although knowing the local penchant for "wacky baccy" I'm afraid that eyewitnesses around here are probably slightly suspect.

GIVE ME THE FACTS

How to get there

The writer flew as a guest of British Airways (0870 850 9850; www.ba.com), which offers return flights from Heathrow to San Francisco from £430.

Where to stay

The Harbor Court Hotel, 165 Steuart Street, San Francisco (001 415 882 1300; www.kimptonhotels.com) offers double rooms from $215 (£113) per night without breakfast. For reservations call 00800 546 78660.

Sanford House Bed and Breakfast Inn, 306 South Pine Street, Ukiah, Mendocino (001 707 462 1653; www.sanfordhouse.com) offers double rooms from $162 (£85) per night with breakfast.

The Grey Whale Inn, 615 North Main Street, Fort Bragg (001 800 382 7244; www.greywhaleinn.com) offers double rooms from $107 (£56) without breakfast.

Carter House Inns, 301 L Street, Eureka (001 707 444 8062; www.carterhouse.com) offers double rooms from $168 (£89) per night with breakfast.

Castle in the Clouds, 7400 St Helena Highway, Napa Valley (001 707 944 2785; www.napacastle.com) offers double rooms from $285 (£150) with breakfast.Two nights minimum.

What to do

Platypus Tours (001 707 631 0757; www.platypustours.com) offers full-day wine tours in Napa starting at $65 (£34) per person.

Balloon Tours with Bonaventura Balloon Company of Napa Valley (001 707 944 2822; www.bonaventuraballoons.com) start from $198 (£104) per person.

Further information

California Tourism (020-8237 7970; www.visitcalifornia.com). San Francisco Convention and Visitors Bureau ( www.sfvisitor.org). Mendocino County Alliance ( www.gomendo.com). Redwood Coast ( www.redwoodvisitor.org). Napa Valley Convention and Visitors Bureau ( www.napavalley.com).