In a trellised drainage pattern, how do tributaries typically join the main river?

In a trellised drainage pattern, tributaries join the main river at right angles. This specific orientation occurs due to the underlying geology and structural features of the landscape. Typically, trellised drainage systems form in areas with a sequence of alternating resistant and less resistant rocks, along with steeply folded strata. The main river flows in a direction that usually follows the geological strike, while the tributaries cut across the valleys formed by the folds at perpendicular angles.

The right-angle junctions create a distinctive and characteristic appearance that is identifiable on maps and aerial photographs. This type of drainage pattern is often found in regions with significant topographic relief, such as mountainous areas or regions that have undergone significant tectonic activity, where the structural alignment dictates the flow direction of both main rivers and tributaries.