Here's why:
* Joints: Joints are fractures in the bedrock that are often perpendicular to each other. They create natural pathways for water to flow.
* Erosion Resistance: The bedrock's resistance to erosion ensures that the joints are preserved and act as the dominant structural control on the landscape.
* Rectangular Pattern: Water flows preferentially along these joints, creating a network of straight, interconnected channels that form right-angle bends, resembling a grid pattern.
Other drainage patterns might be present but are less likely to dominate:
* Trellis: This pattern forms in areas where folded rock layers are exposed, which is not typical for jointed bedrock.
* Dendritic: This pattern develops in areas with relatively uniform rock types, where water flows freely and creates branching channels. This is less likely in the presence of strong structural controls like joints.
* Radial: This pattern develops around a central point, like a volcano or dome. It's unlikely in a jointed bedrock landscape unless a significant topographic feature is present.
In summary: The presence of jointed, erosion-resistant bedrock strongly favors the development of a rectangular drainage pattern due to the preferential flow of water along the joints.
