CALL OF THE CANYON/Raft ride on Colorado River offers exhilarating plunges, serene and leisurely floats, and intriguing hikes on shore where wildlife, still pools, and waterfalls abound

Many people don't realize that a Grand Canyon river trip is not just a 6- to 14-day aquatic version of Disneyland's ``Space Mountain,'' with rafters riding wildly through the rapids the entire time. In fact, river trips afford many quiet hours of just floating along -- time for unusual side hikes, geology and history lessons, camp wanderings, and wildlife watching. Of course, there is a little of ``Space Mountain'' along the way. When I went, the adventurous group, acting like a bunch of high-schoolers gone berserk, was safely led through the rapids of the Colorado River by the boatman's expert rafting skills.

At Hermit Rapid (which rates as a Class IV or V on the International Scale of River Difficulty) we stopped while the boatmen ``read'' the rapid, deciding which was the best way to make it through to the other side. While being reminded of important safety procedures, we quieted our anxieties with the fact that in over 30 years of running the river this company had never had a serious mishap. Approaching the roar of the rapids we felt a curious blend of seriousness and hilarity, as what we were doing did seem a little like Disneyland, it was important to remember that it was not Disneyland.

All this sobered us a little, but certainly didn't spoil our excitement as the roar of Hermit Rapids got louder and the raft floor began to buckle under our tennis shoes. ``Don't hang onto the pontoon ropes!'' the boatman yelled to a student. ``It can shift -- grab the ropes attached to the raft floor!'' A business executive let out a ``Yahoo!'' -- looking more like an aspiring cowboy than the president of a nationwide department store. One of the older women, legs braced against the front of the raft, ``riding shotgun,'' giggled exuberantly as a spray of silty river water washed over us.

We were heading toward a hole in the river that looked big enough to swallow us. Before we could fret over the outcome we slid straight into it, the raft folding, unfolding, and popping out the other side. Even a timid Swiss mother joined in our delighted hullabaloo, chattering in French. We found ourselves floating quietly out the other end before we could register the immense power of the rapids, and the contrasting excitement and quietness became another of the many delights of the canyon.

Although the rapids are the most exciting, the side hikes are the most intriguing part of this trip. The high point of one of our quieter days was stopping at a spot along the river where we hiked up into a side canyon named Silver Grotto. There, we waded through pools and climbed several times up slippery openings into new levels to discover three more pools. Lizards and frogs and an odd insect now and then floated in and scurried about the pools and their slippery side pockets.

The next side hike was to Elves Chasm. It was full of life, cool and blue and green with ferns and waterfalls -- so incongruous with the canyon's deserty starkness. Deer Creek Falls was another stopping point. Here, some of us stayed at the base enjoying the warmer water and listening to the pounding of the falls.

Our last hike was to the boatman trainee's favorite place, a canyon named Matkatamiba. Everyone ventured at least part way up this side canyon, climbing straight up a wedge carved out by a now dry side stream, or walking along the side where there was a more gradual slope. Each hike presented still another one of the quieter sides of the canyon.

The makeup of the tour group generally determines the number of stops for hikes. Not everyone or every group chooses to hike. Some prefer to stay behind in the shade for welcome siestas. Along with business executives and their families, our particular group included a Swiss family; an editor from Mademoiselle magazine; another career women; an ex-preacher turned speech writer and his motorcycle buddy; a few students; and a couple of grandparents. Special-interest groups can also book entire trips as well.

In between rapids and side hikes it was hard to ignore the many different rock layers we saw along the way. In his book ``The Colorado,'' Frank Waters describes the canyon as being like ``The Rocky Mountains upside down . . . a mountain chain, as it were, nearly 300 miles long, up to 18 miles wide, but a mile deep instead of a mile high.'' The different layers of rock spell out over 2 billion years of geological history. A pattern of submersion, deposition, uplift, and erosion was repeated over the centuries: ancient sand dunes, river flood plains, and most of all several submersions under seas account for the deposition of the layers of different types of limestone, shale, sandstone, granite, and gneiss.

The river cuts through these impressive ``pages'' of geological history that go as deep as the beginning of man-recorded time, carrying the observer through all of the earth's changes that happened between the ``beginning,'' as scientists know it, and the age of technology. Waters also compares the canyon with a book a mile tall, with man's 4,000-year history there only equaling the thickness of its last page. Rather than being intimidated by this knowledge, we were awed to be let in on this sight of rock ribbons of reds, greens, light and dark grays, whites, browns, and blacks that seemed to be the primordial sources for all of the colors of the desert artists' paints.

Prehistoric American Indians were the first to inhabit the canyon. Hypothesized to have been 4,000-year-old desert cultures of hunters and gatherers, they left behind split-willow figurines, pottery, granaries, and other remnants for canyon explorers to wonder over.

As for Europeans, the Spanish were the next ``discoverers'' of the canyon, during Coronado's 1540 expedition. Then, in 1869, Maj. John Wesley Powell, a Civil War veteran, ran the first boat expedition/exploration of the canyon. Filled with trepidation, he wrote, ``We are now ready to start on our way down the Great Unknown. . . . Down in these grand gloomy depths we glide, ever listening for the mad waters keep up their roar. . . .'' Less fear-filled times awaited those who, 70 years later (1939), would be buying tickets for river rides. Several years later, two men floated down the river using only neoprene packs on their arms as water wings.

By the early 1970s the river would be nearly overrun with 16,400 people per year, causing the mid-'70s limits to be set at 14,000. This may sound like an overwhelming number of people, but our group saw only a few other rafters and kayakers on the trip. River companies space their trip departures out so that not everyone is in the same place at the same time. And no one but our group ever camped at our campsites, which was another source of the trip's many enjoyments.

An 8 or 9 a.m. start the next morning would have us back on the river. A lookout for wildlife was often requested. Twice, my particular group saw the rare desert bighorn sheep watering near the bank, and we often watched hawks gliding a mile above us near the canyon rim as we floated past. Other rafters have been treated to sights of coyotes, ringtail cats, mule deer, foxes, wild burros, rabbits, herons, egrets, and a variety of water birds.

After having only experienced the canyon for six days, I have to agree with the words President Theodore Roosevelt penned upon seeing the canyon for the first time: ``In [it] Arizona has a natural wonder which, so far as I know, is in kind absolutely unparalleled throughout the rest of the world.'' Practical information:

Trips begin as early as April and run through September. June through August are the best months to go.

You can travel by air or bus from Las Vegas to Lee's Ferry, Ariz., the put-in point on the river. You can also choose between a shorter trip that runs 179 miles to just above Lava Falls (a notoriously hefty rapid) and helicopter out, or go the full 277 miles to Lake Mead and bus out, depending on the outfitter you choose. Trips generally run from 6 to 14 days.

There are several options on crafts: motorized rafts -- you just hang on, with 15-25 people per boat; oar-powered rafts -- you don't help row -- with 4-6 people aboard; paddle crafts -- you do help paddle -- with 6-10 people aboard; wooden dories -- you don't help row -- with 4-6 people aboard; kayaks -- only for the experienced. Costs generally run about $100 a day, which includes food and may include some camping equipment and transportation to and from Las Vegas.

For a list of companies that offer Grand Canyon trips down the Colorado River, as well as other major Western rivers, write or call Western River Guides Assocation, 7600 East Arapahoe Road, Suite 114, Englewood, Colo. 80112, [303] 771-0389, or the American Wilderness Alliance, 7600 East Arapahoe Road, Suite 114, Englewood, Colo. 80112, [303] 771-0380.