We have discussed two of the three major topographic divisions of the park—the high mesas and the benchlands—and there remains to consider the third division—the canyons of the mighty Green and Colorado Rivers and some of their tributaries. After we discuss a few features common to both rivers, we will take up the details of each river. A glance at the map (fig. 1) shows that above the confluence both rivers are very crooked and contain many loops, or meanders, the most striking of which are Bowknot Bend of the Green River (fig. 62), several miles north of the park, and The Loop of the Colorado River (fig. 74). In contrast, the main stem of the Colorado River below the confluence is considerably straighter. Not apparent on the map are the facts that the crooked rivers above the confluence have very gentle grades and are free from rapids or falls, whereas a few miles south of the confluence the main stem plunges into Cataract Canyon—the steepest and wildest reach of the river, containing 64 rapids. These differences are partly explicable on the basis of the geologic structure and character of the rocks through which the rivers have cut. Above the confluence, the soft strata dip gently northward, so in flowing generally southward the two rivers are cutting “against the grain,” which tends to impede their flow and thus reduce their grades. Below the confluence, the hard limestones of the Hermosa Formation lie relatively flat for several miles and then begin to dip gently southward, thus allowing the river to cut “with the grain” and therefore drop more rapidly. The quiet, smooth waters above the confluence permit power boating between the towns of Green River, Utah, and Moab during part of the year, whereas the rapids below Spanish Bottom, 3½ miles below the confluence, restrict river travel to float trips using sturdy boats or rafts. Above the confluence, a so-called Friendship Cruise is run each year during the Memorial Day weekend. Participants tow their own power boats on trailers to the town of Green River, and after the boats are launched, facilities are available at nominal cost for transporting cars and boat trailers to Moab to await the arrival of the boats. Although some high-powered speedboats are reported to have made the run down the Green River to the confluence then up the Colorado River to Moab in a few hours, the trip for most boats requires 2 to 7 days. Trips by power boats, including jet boats, can be arranged from either Green River or Moab. Some passengers from Moab return by jeep from Lathrop Canyon via the White Rim Trail, and some from Green River return on land via the Horsethief Trail. Many prefer the quieter float trip down to the confluence, with return to either town by a prescheduled power boat, and some more adventurous souls float through the rapids of Cataract Canyon all the way to Lake Powell.