A convoy of snowmobiles hurtles along the wide track as forests of snow-dusted conifers rush past. The lead rider raises his arm, gesturing to slow down and then stop. It's a motion that is imitated by each rider until every vehicle is stationary. It's the half-way mark of a two-hour tour of Lake Tahoe's back country. The first stop is at a vantage point with magnificent views of the lake. Undulating snowy mounds in the foreground offer a striking contrast to the forest of green pines, glistening blue water and pale snowcapped mountains beyond. It's a stunning sight, and the only way to get to it is on a snowmobile or skis. The route is a machine-groomed trail known as the Fiberboard Freeway. During the summer months the trail is a popular cycling track frequented by locals and San Francisco daytrippers, but with winter comes the roar of snowmobile engines and the high-speed thrills associated with them. 'Keep away from the grooves in the trail and try to stay away from the trees,' the tour leader, Steve, says as riders fly around the side of the mountain trying to follow his advice. Watson Lake, which freezes over in winter, is an excellent surface for friendly snowmobile races. 'There's not a day that goes by when I haven't seen a rider tumble off their snowmobile while speeding on the frozen ice,' Steve warns. Nonetheless, we hit the throttle and zip onto the lake, cutting fresh tracks across the icy surface. It's so much fun Steve has trouble persuading us to move on to our next destination, which is the summit of Mount Watson, 2,563 metres above sea level. And the view from the top is awe-inspiring. Lake Tahoe is massive - 35km long by 19km wide. It is North America's largest alpine lake, with the California-Nevada state line cutting through its centre. The locals say the water is so pure a white dinner plate can be seen as far down as 25 metres. But even with all that snow, the temperature doesn't get cold enough for this large body of water to freeze over. Steve points out ski resorts in the distance. Like the lake itself, Heavenly Mountain is positioned partly in California and partly in Nevada. The best known resort is Squaw Valley, the site of the 1960 Winter Olympics. High Camp at Squaw Valley has an ice-skating pavilion, a heated open-air swimming lagoon and an Olympic Museum with displays, photographs and paraphernalia from the event. Below the ski slopes, the fairytale atmosphere of Squaw Valley village is framed by picture-perfect snow-covered slopes and has a vibrant apres-ski buzz. Next to Squaw Valley is the Northstar at Tahoe Resort, which is ideal for families and not too expensive. It's hard not to linger, your eyes drinking in the views. On the way back to base, the group is led off the marked trail and into the forest. The snowmobiles race down the side of a steep slope and riders have to work hard to keep their balance and that of their vehicle, using their bodies to change the centre of gravity around the tight turns. The virgin snow streaks past in a flurry. Skiing is a tradition in these white-washed hills, but there's nothing like racing through the landscape on the back of a heaving, rumbling snowmobile to get the heart pumping. Getting there: Cathay Pacific ( www.cathaypacific . com) has regular flights from Hong Kong to San Francisco. If driving from San Francisco, take I-80 to highway CA267. Alternatively, there are ski buses ( www.bayareaskibus.com and www.nacski.com ) that travel from San Francisco to a number of alpine towns, including Squaw Valley.