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31 instead of being carried to the Colorado River as it does now. The .... W reasons for the change in the mode of sedimentation are explained in QO N section 5.4.2. 5.2.4 Hillslopes Hillslopes were studied by measuring cross sections of valleys formed by channels within the eight tributary basins. Table 5.2 reveals the wide range of hillslope gradients within basins and between basins. Although hillslope gradients differ widely, characteristic hill- slope shapes are evident (Fig. 5.5). Figure 5. 5a shows a double- convex valley cross section. This type is characteristic of the upper portions of all of the basins. Figure 5. 5b illustrates the convex- concave type cross section, and it occurs in the middle portions of all the basins. Within the basins, the convex and concave segments of this type alternate on opposite sides of the valleys. The alternation of segments appears to be controlled by the meandering channel con- figuration as opposed to control by either rock type; rock structure, or aspect. Finally, Figure 5. 5c typifies the double-concave cross sections found near the mouths of all of the basins, All three types are nearly equally abundant. Of the 65 measured cross sections, 20 are double-convex, 24 are convex-concave, and 21 are double-concave. The hillslope measurements were Type 6 rill gradient measure- ments. That is, the rills form directly on the hillslopes and maintain essentially the same gradient as that of hillslopes. Schumm (I964) and Lusby, et al. (1971) have studied rill develop men t in the study area. Both investigations revealed seasonal cycles of rill development. Basically, moisture from winter snowmelt associated with freeze-thaw <--- J;\.., ~