Final answer:
A trellis drainage pattern develops over a landscape where the underlying rock structure consists of alternating layers of materials with different resistance, such as medium- to coarse-grained sand and silty clay, often with root structures.
Step-by-step explanation:
The trellis drainage pattern is typically found in areas where the underlying rock structure contains alternating layers of different materials, such as medium- to coarse-grained sand and silty clay. This stratification, often with varying resistance to erosion, leads to the development of a trellis-like network of streams and tributaries. This formation results from the streams' tendency to erode the softer layers of silty clay more rapidly, cutting into them and forming steep-sided valleys. In contrast, the more resistant sand layers form the ridges and high points in the landscape. The presence of root structures within these silty clay beds suggests that vegetation has also played a role in stabilizing these layers and potentially affecting the drainage pattern.