ABSTRACT
Despite very different geologic settings and styles of tectonic disruption, the Nile in Egypt and the Colorado River in the United States and their respective predecessor drainages have many features in common. The most important are 1) they are exotic streams with asymmetric drainage basins; 2) upper reaches of the valleys of each system are geomorphically older than the lower reaches; 3) they have undergone similar episodes of plateau or “Rim” gravel deposition by consequent predecessor streams now disconnected from their source areas; 4) regional drainage reversals occurred early in their histories; 5) early predecessor drainages were controlled by the downdip retreat of resistant cliff-forming units; 6) their configurations were influenced by major drops in base level brought on by plate tectonic events; 7) headward erosion and stream captures became key processes in their final stages; and 8) their aggradation and degradation intervals were determined in great part by alternations between dry and wet climates.
