Final answer:
The underlying rock structure of the rectangular drainage pattern is characterized by horizontal or gently sloping layers of sedimentary rock. This structure is associated with areas where the rock layers have been uplifted or folded, creating a flat or gently undulating surface.
Step-by-step explanation:
The underlying rock structure of the rectangular drainage pattern is typically characterized by horizontal or gently sloping layers of sedimentary rock. This structure is often associated with areas where the rock layers have been uplifted or folded, creating a flat or gently undulating surface. The rectangular pattern itself is formed when streams and rivers flow along the joints and bedding planes of the rocks, creating a grid-like network of channels.