Within the space of a few square miles on a high, boggy plateau called the Chains in southwest England, emerge four rivers. The Exe and the Barle trickle slowly down to the southeast, dissecting the heather moors of Somerset. Their roughly parallel, open valleys become steep and heavily wooded before merging south of Dulverton. Just over the crest from the Barle's headwaters surface the trickles that will coalesce into the West Lyn River. Its short, torrential journey to the Bristol Channel parallels that of Hoar Oak Water, a stream built from three other Chains feeder streams.
An introduction to Exmoor, England's second-smallest national park in Somerset and Devon Counties, might well begin with this remote, quaggy watershed. Brooding in profound silence over the variegated landscapes carved by its rivers, The Chains plateau is the western end of Exmoor's major topographic feature - an undulating moorland platform that plunges steeply toward a rocky northern coast, more gently to the south, where it is creased by the Barle and Exe valleys.
To a hiker on a wet day, the high-flung acres of grass and deer sedge in this area can seem endless. Here one can lose sight of how dramatically landscapes change over relatively short distances within the park's 265 square miles - from moor to wooded valley, valley to rugged coast, even from one moor to another. A few miles south of the Chains, across the Barle, arise hills of vastly different character, slopes blanketed in springy purple heather, which dries quickly after a rain, and bright yellow gorse.
Because of its close-contained diversity, Exmoor is becoming one of British tourism's primary stomping grounds. About a quarter of the park is open moorland , upon which farmers have grazed their stock for centuries. The liaisons between man and moor have their origins in an even remoter past, for literally thousands of barrows, stone monuments, and other Bronze Age archaeological relics dot these uplands. Another 10 percent of the park is natural woodland, concentrated primarily in the river and stream valleys. The rest of Exmoor, including the recently conifered Brendon Hills in the east, is comprised of a human and cultural landscape at least as striking as the river and upland geography that give the area its name.
As is typical of Britain's National Parks, Exmoor is, for the most part, privately owned agricultural land. Many of its hill farms, tucked below the moors in protected valleys, are centuries old, dating perhaps from the Saxon era. Others were more recently carved from the one-time royal hunting preserve of ''Exmoor Forest'' - not a forest at all, but the park's central grasslands encircling and including the Chains. The story of the 19th-century reclamations undertaken by the Knight family, who purchased the land from the Crown, figures prominently in Exmoor's past.
Today Exmoor's hill farms offer some of the park's finest bed-and-breakfast accommodations, in settings at once historically evocative and vibrant with daily activity. They contribute one of the most distinctive features of the park's landscape in the miles of beech hedge that fences and protects livestock. These high botanical weather breakers have irked motorists craning for vistas of Exmoor's heather-clad hills; but they contain their own diverse ecosystems, worthy of close observation.
But to attribute Exmoor's unique flavor to the juxtaposition of natural wilderness and intricately hedgerowed fields is unfair to its villages. These towns and hamlets, with their lovely Celtic or Saxon names, are as unpredictable as the Exmoor countryside. Secluded little Selworthy in the park's northeast corner, with its cob and thatch cottages, is but a few miles from Dunster, whose magnificent castle and deer park afford a bold vista to the sea. The sister villages of Lynton and Lynmouth, 20 miles westward on Exmoor's panoramic coastal road have developed yet a different character, sharing a niche along the craggy coastal cliffs just below Watersmeet, where the East and West Lyn Rivers converge in a rush.
From here a road skirts the east end of the Chains to the tiny haven of Simonsbath. The former home of the Knights in the heart of the old Exmoor Forest , this is the park's historical center. Just a few miles east is the pleasant village of Exford, its geographical center and a favorite rendezvous or ''meet' for Exmoor's mounted hunting parties.
Close to the southern border is Dulverton, with its bustling High Street and old mill. Coach tours of Exmoor leave from here as from other perimeter towns, but this also is a good place to begin a private tour of Exmoor. ''Exmoor House ,'' the park authority's Dulverton headquarters on the banks of the Barle and the major tourist information center, offers a large selection of books on the archaeological relics and living flora and fauna of the park, on Exmoor's villages and inns, on customs and songs, and on roads to take and paths to follow.
From Dulverton the drive across the heather moors southwest of the Barle to Challacombe is among the loveliest in the park, although many claim this accolade for the route just described through the heart of Exmoor - or for the northern coastal stretch. Another favorite is the link between Dulverton and Dunster up the cool, forested Exe Valley, a road with many branches off into the Brendon Hills, rich with the lore of a former mining industry.
A number of beckoning side roads off of Exmoor's major arteries take one deep into the moors or into small wooded valleys. One loved by ''Lorna Doone'' fans leaves the coastal road a few miles west of Porlock to wind through the lovely Oare Valley immortalized by R. D. Blackmore's novel. A detour from the main road over Winsford Hill between Exford and Dulverton dips into Winsford itself, a village with a splashing ford across the Exe and a lovely thatched inn. Southwest from the hill is Tarr Steps, a footbridge of huge stone slabs constructed, it is thought, during the Middle Ages, or perhaps much earlier.
Many of Exmoor's highlights lie off the paved roads, and the park has evoked the strongest response from those who see it by foot. Even short hikes from a parked car offer special and abundant dividends, and lunch or afternoon tea are never far away for subsequent refreshment.
It is important to know your limits as well as your interests, for the park contains some 600 miles of signposted footpaths over land purchased and protected by the National Trust or park authority or along rights of way with private landowners - who, incidentally, expect gates that are opened to be closed again.
One of my favorite hikes leads from Porlock Weir to a glade high above the Bristol Channel, shared by a tiny cottage offering afternoon tea and Culbone Church, which is possibly England's smallest parish. Near the church is a family pottery with a sales shop. But remember, no public road leads to Culbone. One of my indelible Exmoor memories was born the day I helped a friend tote a large ceramic urn on a gingerly return down to Porlock.
It is difficult to leave Exmoor without following one of the paths to Dunkery Beacon - however many times one has walked here before. The park's summit at 1, 705 feet (100 feet above the Chains summit), this is spectacular heather moorland with sweeping vistas.
For those who may prefer to explore some of the park's less-beaten paths, it is worth purchasing a compass and a topographical ordnance map that marks footpaths in dotted-red lines. The mists can gather quickly over Exmoor's ancient barrows.
What is the best of Exmoor? The answer is highly personal and any choice should be tempered by the knowledge that this area continues to surprise even those who know it well. Looking over my now scruffy map, I see how much more there is to explore - places like Smallacombe and Moles Chamber Raven's Nest above the Exe, and Great Staddon Hill - all the inner spaces and wild open places I have yet to discover there.For more information on Exmoor, contact the British Tourist Authority, 680 Fifth Avenue, New York, N.Y. 10019, requesting information about England's west country and about overnight stays at farms.