After a few days in the canyon, the river's rhythm takes over completely. Time's passage is measured with each bend as it opens up a new vertical stone world bounded by the butterscotch-colored water and a distant window of burning blue sky.

For 20 million years, fed by Colorado Rocky Mountain snows and thunderstorms, the San Juan River has been carving into southeastern Utah's huge, uplifted sediment beds. At its deepest part is an exceptionally sinuous series of meanders called the goosenecks, sheer 2,000-foot walls that tower above a river bed only 50 to 100 feet wide. Here the canyon's heart is cut into 300 million-year-old limestone deposited beneath ancient inland seas.In the face of all this power and endurance, reflections of fragile wanderers drift along in vinyl bubbles. The strong feeling of isolation inherent in a deep canyon makes the experience all the more surreal.

The only havens for landlubbers are the sandbars. They range from slivers barely wide enough to be called terra firma to relatively large plots acres in size. These are covered with spring green cottonwoods, salt cedar, sage and blossoming wildflowers. Protected and warm, the canyon floor's plant growth is weeks ahead of the higher altitude, blustery, early spring rim.

The trip is a 60-mile, five-day float trip from the the Mexican Hat Bridge in Utah about 70 miles from the Colorado border to Clay Crossing, where the San Juan empties into Lake Powell.

It's a "float trip" in the true sense of the word, as opposed to "white water." We will run only a half-dozen rapids on the whole route.

In contrast, the Taos Box Canyon of the Rio Grande. In 18 miles there are dozens of rapids; "The Rock Garden," is two miles long.

The lack of white water makes way for other diversions, such as side canyon exploration. There are three major sidetrips on the route. Two are Johns Slickhorn, which can be walked for 15 miles, and Grand Gulch, which can be followed for more than 60 miles.

Fantastically colored rock forms, lush spring-fed fern gardens, crystal-clear swimming holes, petroglyphs and ancient stone ruins are some of the treasures hidden in these canyons.

Even though many people float the lower San Juan, the river remains pristine. The rim area is inaccessible and only one trail goes to the canyon bottom in the whole 60 miles.

The San Juan was the last of the Utah canyonland rivers to be explored. Recreational rafting didn't start here until the 1930s.

In one sense, the freedom gained in floating the San Juan is an illusion. Any long raft trip requires quite a bit of logistics. Transportation to the entry point and from the exit point needs planning. All shelter, food and water has to be carried on board, as do safety and raft repair equipment.