Yellowstone in winter is crystal and steam. In summer the national park is Nature with a capital N: thick forests, certain stands seared by recent wildfire; flower-splashed meadows; graceful rivers and lakes; wild-yet-warily-patient creatures; and, as always, bubbling, sputtering volcanic mysteries.

In spring - the near-forgotten season - Yellowstone in transition is all of these things and something else: a maternity ward as big as all outdoors.Soft-brown baby bison nuzzle great shaggy black-brown mama buffalo. Canadian geese settle down to nest, and goslings appear. The abundant elk, too, begin to give birth to a new generation.

"Last May 15th I was leading a tour of kindergarteners and we saw an elk calf being born," remembers Park Ranger Caroline Evans. "We watched for 30 minutes."

She's sure the awestruck children will never forget the sight. As the meadow grasses get thicker with summer's approach, the calves are better concealed, she says; later visitors didn't see what they saw.

But in spring the birds and animals - swans and pelicans and ducks, deer and moose, even bears, if you're alert, in the right place at the right time or maybe just up early enough - seem to be everywhere.

People, on the other hand, are downright sparse. The whole sanctuary is a little quieter. A few tourists, especially in late April and early May, have the whole place to themselves.

Spring officially arrives in Yellowstone when the roads begin to open to vehicles - this year that was May 3. Sometimes the higher passes, like Dunraven, need a few weeks more, says Marsha Karle of the park's public affairs office. But really some access is possible even earlier most years from West Yellowstone, Mont., and especially on the north end, through Gardiner, Mont., and Mammoth Hot Springs and through Cooke City, Mont., on the northeast.

"The opening is a gradual process throughout May," Karle says, partly tied to the melt of the winter's snowpack. "Spring can go until just after Memorial Day weekend, when we start getting real busy."

The Yellowstone experience at this time of year differs from visits in other months. A few of the stores inside the park are doing business, but a great many facilities - lodges, trails, concessions - just aren't open yet, although rooms, restaurants and such are available in communities bordering Yellowstone.

Still, beating the pre-summer crush has its rewards. An early May trek on the trails overlooking the Grand Canyon of the Yellowstone, for instance, can be enjoyed in nearsolitude. You can almost imagine the peace and inspiration Thomas Moran enjoyed at Artist Point and other overlooks below the Yellowstone River's Lower Falls when envisioning his grand paintings over a century ago.

In May, the north side of the yellow-, red- and orange-streaked chasm is usually free of snow, but on the south walls snow remains in swaths and patches. Far off, the falls boom and mists rise. Vistas and solitary peace - in what is otherwise one of the most-visited wild places on the planet.

The same is true of Old Faithful and in the geyser basins. The picture-perfect settings star snow and new-green grass, clouds of steam, prismatic ponds, animals in a variety Noah would envy - and remarkably few Homo sapiens.Spring weather is unpredictable everywhere, but notoriously so in Yellowstone. Summer may be just around the corner, but winter likes to get a late word in now and then.

"Spring visitors should plan to take good equipment - jackets, mittens, hats, the works - for possible cold weather," Ranger Caroline Evans cautions. "In fact, that could be true in July . . . ."

There have been spring snowshowers recently, but overall the temperatures have been quite mild and haven't dropped below freezing, she says.

According to the latest information on roads, the Mammoth to Norris highway and west, east and south entrances are all open. The Old Faithful to West Thumb route is set to open, weather permitting, on May 20, the Beartooth Highway on May 25 and Tower Junction to Canyon on June 1.

The Mammoth campground is open year-round and the Madison campground opened on Friday. The Norris campground opens May 17, and the facilities at Bridge Bay, Slough Creek and Tower Fall open May 24. Others open in June. Fees range from $8 to $10. All except Bridge Bay, which has a partial reservation system, are available on a first-come, first-served basis. Fishing season begins in some waters May 25.

Yellowstone - established as the world's first national park in 1872 - is noting the 75th anniversary of its guardian, the National Park Service, this year. Yellowstone was managed by the U.S. Army until 1916, when national park rangers first reported for duty. Yellowstone employed 22 rangers in 1916 and had almost 36,000 visitors. The park now employs 300 permanent employees and welcomes more than 2.6 million visitors each year.

Here are some of the activities under way in Yellowstone during upcoming weeks:

- On Tuesday, May 7, the Imagine Yellowstone Arts Festival kicks off with the "Celebrating Our Parks" exhibit in the Albright Visitor Center at Mammoth Hot Springs. "We invited children from all over the country to enter their artwork on what their undertanding of the park was," Evans says.

- On May 18, the "Yellowstone and Fire" exhibit, first displayed last year to explain the extent and importance of the 1988 wildfires, opens at the Canyon Visitor Center.

- On May 22 the park celebrates the centennial of the Lake Hotel. Wyoming Gov. Mike Sullivan will officiate at an 11 a.m. ceremony, and exhibits will show what it was like to visit Yellowstone Lake and the park 100 years ago.

- On May 28 at 10 a.m., Yellowstone opens the Children's Fire Trail on the park's north end between Mammoth and Tower. Much of the funding for this explanatory trail came from children interested in the 1988 fires and their impact, Evans says.



Yellowstone phones

Planning a Yellowstone vacation? Here are a few phone numbers (all long-distance) that might prove helpful in organizing your trip:

- National Park Service, and for current road and weather data: (307) 344-7381. A recording gives instructions on various digit codes you can punch for more information or help.

- TW Recreational Services, for lodge accommodations within the park: (307) 344-7311. (Old Faithful Inn has opened; other facilities begin opening in late May.)

- West Yellowstone Chamber of Commerce: (406) 646-7701.

- Jackson Chamber of Commerce: (307) 733-3316.