It's not a long river trip. Under power, half a day will do it. It's not a particularly nerve-wrenching trip, either. Aside from a couple of ripples, the water's as calm as a sleeping dog. And it's not difficult to take. Anyone with a boat, with or without a motor, can make it.

Still, there's something thrilling about lazily floating the Colorado River through the last of Glen Canyon, possibly because it's the last of what Lake Powell was. Then it could be because it is so easy. Or, it could be the overwhelming power of the red rock walls, and the obvious strength of the river.The river ride goes from the Glen Canyon Dam to Lees Ferry, about 15 miles as the river winds, less than half that as the crow flies. There are morning and afternoon runs, and all-day trips. It starts where the dam stops and ends when the Grand Canyon starts at the old ferry site.

According to Dean Crane, general manager of Wilderness River Adventure, over 24,000 people floated the river last year with his company. More are expected to float it this year. All the outfitters combined will only take about twice that number down the famed Grand Canyon river run.

There is something special about this small stretch of river.

There are, in fact, three accepted theories to the canyon's creation:

1. The river cut through the rock.

2. The rock pushed up along the river.

3. The river cut down as the cliffs shot up.

All three sound reasonable . . . formidable river protected on two sides by 500-foot roughly carved cliffs. One up, one down, or down and up. Anyway, the result is a beautiful stretch of river marked by awe-striking rock wall, a mixture of sandy beaches and tamarisk-choked shorelines, and a clean, green-hued river that confidently pushes its way towards the Grand.

The trip begins with a drive down a two-mile tunnel cut in the rock wall that angles from the butte to the base of the dam. It was built to get workers to the base of the dam back in the early 1960s.

John Wesley Powell, first to explore the Colorado River, reached this point back on Aug. 4, 1869. His report was:

"After dinner we find the river making a sudden turn to the northwest, and the character of the canyon changed. The walls are chiefly shales of beautiful colors . . . Here the canyon terminates abruptly in a line of cliffs."

Today, Powell would see the colors and the cliffs. He would, of course, see the dam and, now, a fresh-running river. When Powell passed through it was a silty-brown. It is estimated some 168 tons of silt a year floated down the river before the dam, three times that in high runoff. Now Lake Powell stops the silt and returns only chilling (45 degrees), clear water.

Which, of course, has helped turn the stretch of river below the dam into what was once called the finest trout stream in the country, and is now classed as a very good one. Rafters float down the river now and see the river rainbows streaking out of their way, while fishermen come up-lake and try to catch them.

Boatmen reported that two weeks ago a six-pound trophy was pulled in by a fly fisherman. Ten years ago, it likely would not have been worth mentioning. This was a section of ideal habitat and big fish.

Seven miles down the river, on a reddish limestone wall behind a sandy beach, are hidden signs of early man. Petroglyphs, according to one interpretation, show men, young and old, herds of sheep, possibly deer, paths down into the canyon and up again, and possibly death.

A few miles more, and off to the left, is Stanton's Cave. Given a claim to mine gold and required to make $100 in improvements, Robert Stanton built a road to his cave. Stanton, an engineer, came to the river with Frank Brown in hopes of finding a railroad route through to link Colorado and California. Brown died in a boating accident and Stanton came back to mine and live in a cave.

Near the end of the trip, off to the right in waist-deep water, are the remnants of the coal-hauling steamboat of Charles H. Spencer, another early miner. The old boilers and paddle-wheel gears are out of the water, the skeletal remains of the hull under the surface.

A few hundred yards down river is the ramp at Lees Ferry. The site was, for many years, the only Colorado River crossing for 500 miles around. The ferry was operated at first by John Doyle Lee, who later was executed for the Mountain Meadow Massacre of 1874.

Men, animals and machines were ferried across the river here until 1929. On its last voyage, three men and two Model A Fords were lost. A year later, a bridge was built to link the canyon walls.

From Lees Ferry, it's a one-hour bus ride back to Page. Half-day travelers see as much as full-day. Longer trips merely float more, have lunch and stop to see more sites.

All-day trips are $41.95 for adults, $20.95 for children; half-day cost $24.95 for adults and $16.95 for children.

One thing that adds to the popularity of this trip is that long-range plans are not necessary. Crane said a phone call the day before is sufficient. It fits well, he said, into the schedules of people coming to Lake Powell "and looking for a beautiful, restful experience."