Ski dream. Back in 1937, a man with homemade skis and a vision rigged a tow rope to his Model A Ford truck, and Mammoth Mountain Ski Area was born

THE legend of Dave McCoy and his beloved Mammoth Mountain in California's eastern Sierra has been told around fireplaces at apr`es-ski gatherings throughout the West. But this season there's a new chapter. What has long been the busiest ski area in the nation may now be the largest as well. Last June, Mr. McCoy purchased the neighboring ski area, June Mountain, with an intent to link the two, which means a potential of six times the skiable terrain of Mammoth's already sizable acreage. It's a coup that adds to his stature among ski folk.

The tale begins nearly 50 years ago, when this rugged mountain man strapped homemade skis on his back and hiked off into the wilderness to develop a ski resort. He had never been to one. He had never ridden a ski lift.

But he skied, every day. As a hydrographer with the Los Angeles Department of Water and Power, he skied deep into the Sierra to measure the snow and determine its water supply potential. He learned about the mountains -- where the first snow fell, where it lasted longest, what slopes were most challenging.

In the summer of 1937 he drove a 1927 Model A Ford truck up a slope and left it. He chose a place with the earliest and best snow, with the greatest vertical drop in the shortest distance.

When winter came, he jacked up the back wheel and fastened a long loop of rope around it, rigged the other end to a tree, and announced the first rope tow in the eastern Sierra.

People came. More rope tows followed. More people came. He rigged seven tows in tandem - nearly 2,000 feet - up to a rugged ridge with a snarling lip of snow overhanging a natural bowl. Before there were permanent roads, McCoy towed people in and out with weasels - Navy surplus tracked vehicles. ``In those days we knew everybody who had a pair of skis in California,'' McCoy says quietly. ``And everybody helped. People packed the runs by skiing them. When we needed a rope spliced or gas hauled to the top, there were always volunteers. When we had mechanical problems, everybody sat down on the snow, had a picnic, and sang. If it snowed while we were skiing, people pulled the buried cars out with ropes. No one left until everybody was out. That's what this place is made of.''

That snarling lip of snow discovered in the '30s, the Cornice, like McCoy himself, is legendary among Western ski folk. Though its relentless mogul field on the steep looms large in nearly every Western skier's memory or hopes, it's not the most treacherous. Other runs known to locals by ominous names like Dragon's Back, Paranoid, Wipe Out, and One Chance are more so.

But a mountain so large has many moods. It can be playful or smooth. Trails like Hansel and Gretel weave gently through stands of evergreen, and pre-ski instruction for toddlers occupies sheltered fenced-in areas. With 150 runs, there are many for every level of ability. Roughly 30 percent of them are advanced or expert, 40 percent intermediate, and 30 percent beginner.

The mountain is crisscrossed with a network of chairlifts numbered in the order they were built. Newcomers better carry trail maps -- and shouldn't expect to ski the whole mountain in one day. Chair 1, which takes off from the site of the early rope tow tandem, is especially popular. By using it, experts can either plunge down Gravy Chute or weave through an apron of bubbly mogols called The Wall, while their intermediate friends can coast the wide, smooth Broadway - and both can meet at the bottom to ride back up together.

Equally popular, Chair 23 rises 1,100 feet in a distance of 2,629 feet. Skiers on this cushy triple chair are sucked up into a weather shelter at the top that looks like a huge vacuum nozzle. The 360-degree view from the 11,053-foot ridge is spectacular - to the northeast there's Nevada. But better concentrate on the way down - or on one of half a dozen ways down. The Mammoth skier continually makes choices.

McCoy's Mammoth Mountain, leased from the United States Forest Service, draws an average of 17,000 skiers on a good weekend. Mammoth's own 25 chairlifts, one gondola, and four surface lifts carry an hourly uphill capacity of 42,000 skiers to 1,330 acres of bowls, ridges, and trails. Add to this the five existing lifts at June Mountain, and McCoy's new June developments: a 10- to 20-passenger aerial tram and a detachable quad chair, the longest lift in California (9,000 feet) - all available this season on an interchangeable lift ticket. A staff of 200 instructors plus a separate team of recreational racing instructors swarms over the mountain from Thanksgiving to July Fourth. Mammoth has become the recreational racing headquarters for the West, and the Olympic team has made it its spring training ground.

Ever since McCoy's wife, Roma, collected 50 cents from skiers at the base of a tow rope so she could buy groceries and gas for the tows, Mammoth has been a family business.

``And it'll stay that way,'' McCoy affirms. Other resorts of comparable size are owned by corporations, but McCoy's connection with the mountain is firm, intimate, and daily. At 5:30 on a winter morning he's already peering across the upper ridge, supervising avalanche prevention. Later he might be teaching his grandchildren to race, or coaching an Olympic hopeful - or racing himself. He holds the 1984 Masters downhill title in his age category.

You may find him talking to skiers in line or to lift operators (he's on a first-name basis with 1,400 employees). Or he may be doing his favorite thing -- skiing with his wife. Last summer he was as excited about carving out new runs at June Mountain as he was when he first saw Mammoth in the '30s and had the vision of a resort. ``It's the personal interest he takes in the mountain and the skiers' experience that makes this place special,'' lift operators say.

No wonder a town has grown around him. Mammoth Lakes, now with a winter population of 7,000, can accommodate 36,000 visitors in its condos and hostelries. Every winter Friday night a stream of headlights threads its way through the desert from Los Angeles, six hours to the south. It's southern California heading for the hills that were once thought too high, too remote, too stormy to ever become a going resort. Practical information. For more details contact Mammoth Mountain Ski Area, PO Box 24, Mammoth Lakes, CA 93546.