INDEPENDENCE OF CONTINENTAL DIVIDE TRACE COMPLEXITY FROM TOPOGRAPHIC RELIEF

Map-view trace complexity of the Continental Divide in the conterminous U.S. varies considerably along its length, with no discernable control exerted by topographic relief, and little by host physiographic province. This study evaluates local degree of irregularity in the Divide path for 65 segments of the Divide, comprising the full length stretching from southern New Mexico to northern Montana. The complexity measure used is CT_{1-10 km}, percentage difference in length estimates for the trace obtained by divider walks at 10 and 1 km step sizes.

Complexity values for the Divide trace segments range from 3% to 45%, approximating normal distribution around an average of 23.5%, with some bimodal character introduced by a lack of cases in the near-peak range 24.5-26.5%. Segments in lowland, moderate-relief, and mountain terrain show little variation and no consistent trend in mean trace complexity value, and an array of Divide segment relief and elevation measures account for an insignificant amount of variation in complexity (R² values less than 0.04).

Analysis of terrain characteristics associated with the 65 Divide segments identifies some factors favoring especially low, and especially high, trace complexity of these watershed boundaries. Segments traversing valley areas, as well as those in zones of Quaternary volcanism, show multiple examples of low extremes of trace complexity (CT < 15%), and also of high extremes (CT > 29%), but no cases with more moderate degrees of complexity. The meanCT value for ten segments within the Colorado Plateau is notably lower than for other physiographic provinces. Results for small numbers of cases suggest very low degrees of complexity for divide traces running between parallel drainages on fans and pediments, and high complexity for segments traversing areas of mapped planar intrusions.