Flights are best right after sunrise, when the air is calm and cool.
Sometimes there's a catered champagne brunch at the end of the adventure. At a dozen or so places you can immerse yourself in the mud, followed by a mineral-water shower and a whirlpool bath, and then a steam bath. It's perhaps the most relaxing experience in California. The fastest flows are in the spring, naturally. Depending on the river and the time of year, some trips are okay for children over 6.