Giant cacti and sky islands - now that's some trip

The pan-flat deserts and mighty mountains of south-east Arizona must be seen to be believed. Steve Connor sets off on horseback

Some 27 million years ago in what is now south-eastern Arizona, a supervolcano exploded with such force that it enveloped the surrounding area in 2,000 feet of molten rock and ash. Today, that layer - long since solidified, cracked and eroded - has weathered away unevenly to form a vast forest of stone columns and other weirdly petrified shapes, some precariously balanced like spinning tops on a pole. I'm standing on the top of one of them and can hear nothing but the faint whisper of wind and the raucous cackle of a raven, which echoes eerily in the canyons below.

Some 27 million years ago in what is now south-eastern Arizona, a supervolcano exploded with such force that it enveloped the surrounding area in 2,000 feet of molten rock and ash. Today, that layer - long since solidified, cracked and eroded - has weathered away unevenly to form a vast forest of stone columns and other weirdly petrified shapes, some precariously balanced like spinning tops on a pole. I'm standing on the top of one of them and can hear nothing but the faint whisper of wind and the raucous cackle of a raven, which echoes eerily in the canyons below.

These are the Chiricahua mountains, and from the highest points you see why these and the other vast outcrops of rock in southern Arizona are known as "sky islands". From my perch some 7,000 feet above sea level I can look north-west towards Tucson, which lies behind the Mica mountains, 40 miles away. In between squats the low, deserted plain of Sulphur Springs Valley. Like much of south-eastern Arizona, the landscape is composed of pan-flat deserts which act like oceans separating the isolated mountain ranges that shoot up to the sky like true desert islands.

The sky island of the Chiricahuas is one of the most stunningly beautiful places anyone can hope to see. It was once the stamping ground of the fearsome Chiricahua Apaches whose chief, Cochise, built his last stronghold not many miles away. In fact, it is said that his resting head can be seen in the outline of one of the Chiricahua summits - a fitting monument perhaps to a man whose people were long ago banished to a distant reservation.

This is the final day of my journey through south-eastern Arizona, a corner of the Grand Canyon state often overlooked by travellers heading north to view its most famous attraction. It is a journey that started a week earlier on the other side of the Mica mountains.

I woke up one morning to find myself riding through the Sonora desert where the giant saguaro cactus emerges from the ground like spiky, green fingers. This is the landscape of Hollywood westerns, and what better way to appreciate it than on the back of a horse. Roger the wrangler led the way, which was fortunate because this is only the second time in my life that I've ridden. Roger works on the Tanque Verde Ranch a few miles east of Tucson, which specialises in desert horse-riding and nature trekking. He tells me that he once tracked a mountain lion through this landscape for 16 days, which I can believe. Think Marlboro Man and you have a fair idea of Roger's general demeanour.

During my stay at Tanque Verde I rode three horses in turn, and by the time I got to Puck, my third, I had acquired the necessary basics of equine control. A gentle kick and he was off. A firm tug on the reins and he stopped. Flick the reins left and he went left, flick them to the right and he turned right. It was as easy as driving an automatic Chevy, although not as soft on the hind quarters.

Yet riding through the Sonora desert is probably the best way of experiencing it. You can see much further than if you were on foot. While your horse keeps his eye on where he's going, you can concentrate on the breathtaking scenery. The saguaro cactus is the most obvious manifestation of this arid habitat. These leviathans can live for hundreds of years and can swell after a rainstorm to weigh seven tons, holding enough water to survive two years of drought.

From astride Puck I saw a grazing mule deer and a rattlesnake. I also saw mountain lion, lynx, black bear, desert coyote, brightly coloured humming-birds and prairie dogs - not, I have to say, while riding, but on a visit to the Arizona-Sonora Desert Museum a few miles west of Tucson. A visit to this delightful and tastefully designed nature park is obligatory for anyone who wants to understand how the local flora and fauna are adapted to the harsh conditions of desert life.

Water, or rather the lack of it, dominates the Arizonan environment. As the name of the state suggests, this really is an arid zone. There are five seasons: winter, spring, fall and two types of summer - dry and monsoon. Most of the useful rain falls in widespread winter showers but the monsoon thunderstorms can bring torrential downpours and flash floods. It was strange driving through the dry heat of a November day past flood warning signs.

Driving south from Tucson, I was soon on my way to visit the first sky island of the trip. As the car climbed higher, the saguaro cactus gave way to parched grassland and a hint of cooler air. I was travelling south yet the climate became fresher as the car climbed higher. On the horizon I saw my destination, the magnificent Huachuca mountains, which rise abruptly from the surrounding plain. This part of Arizona is renowned as one of the most ecological diverse regions of North America. It sits at the crossroads of four distinct eco-systems - the Sierra Madre of Mexico, the Rocky Mountains to the east, and the Sonora and Chihuahua deserts in the north and south respectively. Through this complex sandwich of habitats runs the San Pedro river, one of the few in the United States where the water flows north. For thousands of years the San Pedro has irrigated a verdant streak of vegetation that has acted as a highway for migrating animals - and humans - on their north-south journey. Naturalists have nominated it one of the "Last Great Places" on earth.

Something like 450 species of birds use the San Pedro valley as a flight corridor, and the area around the town of Sierra Vista in the foothills of the Huachucas is an avian paradise. Many of them stop off for more than rest and refuelling - some 150 species nest here. It's not only birds that love this area. In one canyon alone naturalists have recorded 100 species of butterfly, including the famous monarch which appears in the San Pedro valley on its epic migration from the Canadian border to Mexico.

I spent one afternoon walking along the banks of the San Pedro with volunteer guide Dutch Nagel, who retired to this area. Dutch told me that the San Pedro was once known as Beaver river because of the thousands of beaver that were regularly trapped for their skins. Eventually, inevitably, they became extinct. A recent re-introduction scheme seems to have taken off - the 15 beaver introduced have multiplied to 75. Dutch showed me some of the trees cut down by the beavers, and a "lodge" that one family had built for itself.

A good way of experiencing the full splendour of the Huachucas is to take a day's hike up one of its many canyons. These are not the arid canyons you normally associate with Arizona. In fact they are more like the sort of tree-lined, hill valleys you see in Yorkshire or Scotland, minus the drizzle. Ramsey Canyon, for instance, on the eastern slope of the Huachucas, is delightfully sprinkled with oaks, mesquite and cottonwood trees, although the occasional prickly pear cactus reminds you that the desert is not far away.

Some of the canyons have visitor centres at the start of a trail, and the Nature Conservancy in Arizona has one in Ramsey where "docents" - volunteer guides like Dutch - are on hand. As well as being home to 14 species of humming-bird, Ramsey Canyon was, more than a century ago, centre of a thriving mining community. It is hard to imagine that there was once a small village in this quiet paradise, complete with bar and dance hall. A few remnants of the wooden buildings remain; many have been removed to return the canyon to its original state.

People have enjoyed the pleasant climate of the sky islands for thousands of years. Garden Canyon, which is accessed through Fort Huachuca, a US military base and once home of the African-American "buffalo soldiers", has some of the best ancient rock art in the region. Walk far enough up the canyon and you reach a leafy glade with a murmuring stream, where an overhanging rock on a cliff face has sheltered generations of native Americans. On the walls and ceiling they have painted pictograms of golden eagles, mystic whorls and spirals, masks and dancing shamans. Little is know about what the images represent, Charles Slaymaker, a US Army archaeologist, told me. One theory is that the rock shelter was used over the centuries by the Hohokam people and the Apache tribe in their fertility rituals to mark the onset of puberty.

At Murray Springs, towards the San Pedro, it's possible to walk even further back into prehistory. Petroglyphs - ancient rock art etched into stones and cliffs - pepper the trail. Finds date back at least 11,000 years when the Clovis culture hunted mammoth and bison.

A two-hour drive from the Huachucas and I arrive at my final destination, the Chiricahuas and the Sunglow Ranch, built on the site of the volcanic caldera whose eruption27 million years ago formed the surrounding landscape. The fresh air and silence prove the perfect tranquilliser. It is not every night I can say I slept in the jaws of an extinct volcano.

GIVE ME THE FACTS

How to get there

British Airways (0870-850 9850; www.ba.com) offers return fares from Heathrow to Phoenix from £433.

Enterprise Car Rental (0870-350 3000; www.enterprise.com) offers one week's car hire in Arizona from $199 (£105).

Where to stay

Tanque Verde Guest Ranch (001 520 296 6275; www.tanqueverderanch.com), Tucson, offers double rooms from $451 (£240) per night, full board , including all ranch activities. Sunglow Guest Ranch (001 520 824 3334; www.sunglowranch.com), Pearce, offers one-bedroomed casitas from $234 (£125) per night. Rail Oaks Ranch (001 520 378 0461; www.railoaksranch.com), Huachuca Mountains, offers double rooms from $154 (£82) per night with breakfast, based on two sharing.

Further information

Arizona Office of Tourism (020-8741 7256, £1.50 per min; www.arizonaguide.com).

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