Boulders big as a house dot the barren, rocky landscape. And there is no obvious track ahead, even though this is the start of the grand-daddy of all off-road trails. I knew it was going to be tough but I just couldn't believe the harshness of the terrain ahead. "Would you like to drive first?" says my driving partner - a dead giveway that she is just as alarmed about the challenge we are embarking upon, writes Claire Bowen.
Bravely I climb aboard the 4-litre Chrysler Jeep, with its protective strips of metal (called rock rails) on the bottom part of the doors and armour plated underside, and prepare to tackle the Rubicon Trail. This 19-mile trail across America's Sierra Nevada mountains takes almost two days and has a reputation as being the toughest in the world.
We are among the 1,000 brave souls taking part in the Jeepers Jamboree - most of the teams in their own vehicles. Before we get under way, Bart, the shaggy-bearded Jamboree leader, has a few words of advice: Drive slowly and follow the instructions of the guides who will pop up at each difficult section - and don't damage your pumpkins by straddling rocks. Yes, pumpkins - they're differentials to you and me. Each group of around a dozen vehicles is led by an accomplished trail blazer equipped with ropes, pulleys and all the gear needed to drag one of his novices out of trouble.
My heart is in my mouth as we pull away slowly across this granite terrain. It's traversable for a couple of months a year - the rest of the time it's either under water or snow. Horrible noises come from the underside of the vehicle as it wacks the boulders underneath. No matter how slow or careful, you just can't avoid making contact with the unforgiving rocky surface.
Because of the severity of the terrain we engage four-wheel drive, low ratio and are advised to stay in first gear throughout - even if we think the surface has improved. For the next seven hours we scramble up smooth rock surfaces, climb hills so steep that all we can see is the sky, bounce between boulders, cross rivers, slide along sand-covered river beds and become overjoyed when we spot some muddy ruts. At least these are familiar territory to any Irish off-roader.
Along the way our guides pop up heralding an extra tricky manoeuvre. Patiently they guide us forward or tell us to "Back up" or "Cut right or left". And we are unduly proud when they exclaim in their west coast drawl: "You got it" or "Good job".
By the end of the day we trust them implicitly but we award star points to Troy, a tall blond with handsome cowboy looks whose instructions are so clear he keeps us and our Jeep out of trouble and helps us make light of the most difficult task.
All day the sun shines from a cloudless blue sky. And, despite travelling through the most spectacular scenery, the only chance we have to enjoy the views is when it's your turn to co-drive.
We are immensely relieved to arrive exhausted but intact at our overnight halt at Rubicon Springs. Here the biggest juicy steaks imaginable are being cooked on a giant barbeque, turned and poked by what looks like a cattle prod by the Sheriff of Eldorado County and his jolly catering crew.
After a wash in the Rubicon river - blissfully unaware of the snakes hiding in the murky depths - we queue for dinner with our fellow Jeepers and enjoy an evening of chat and music around a colossal bonfire before climbing wearily into our sleeping bags.
Brown bears hunting for food are another danger in these parts and we are warned not to take any food to our tents. I expect to spend the night awake listening for bears and hope to take a peek in safety at the furry creature. But exhaustion takes over.
Just as well . . . by 6 a.m. the next morning we are on our way again, boulder hopping back to civilisation. But before the going gets smoother, though not exactly tarmac flat, we face the sting in the tail. Cadillac Hill is a steep, muddy and rocky ascent at the side of a cliff. A wrong move and . . .
Thankfully our guides are on hand and we watch them like hawks. One particular section demands a sharp turn left almost touching the rock face before a sharp right which brings the vehicle to the edge of the cliff and elicits a terrified whimper from my co-driver who is virtually hanging over the edge.
Today's terrain is vastly different from yesterday's rocky wilderness. Flower meadows, fir tree forests and lakes covered in lily pads give way to the former desolation. But the going stays tough.
Six hours later, all the Jeeps draw into a large tarmac-covered car park. Here we raise and clean our dust-covered windscreens and prepare to return to our base on the shores of the stunningly beautiful Lake Tahoe. Ahead lies a 40-minute drive on normal roads and a welcome shower. Now fear has turned to delight. We've conquered the biggest and baddest off-road trail in the world and collected a store of lifetime memories.
Lowdown on the Rubicon Trail
• All Chrysler Jeeps, even Grand Cherokees, must be capable of completing the Rubicon Trail. Chrysler engineers test these legendry off-roaders on the Trail which was once used by Indians.
• Automatic transmission was fitted to our vehicle as the demanding route can result in burnt-out clutches when driven by those unused to the very harsh terrain.
• Mark A Smith started the Jeep Jamboree along the Rubicon Trail in 1952. Jeep Jamboree USA was founded 30 years later and is now run by his son Greg - who accompanied us on the Trail - and his daughter Jill.
• 35 trails are organised each year all over the US. Their difficulty is rated on a scale from 1 to 10. The rubicon is the only 10.
• You can hire a Jeep to take part in some of the trails - but not the Rubicon.
INFORMATION:
Jeep Jamboree USA. Phone: 001 530 333 4777
Website: www.jeepjamboreeusa.com. E-mail: jeepjam@jeepjam.com