Final answer:
The youngest flat lying rock layer exposed in the Grand Canyon is the Kaibab Limestone. It is the uppermost layer in the geological sequence, with other formations like the Toroweap Formation and Coconino Sandstone beneath it.
Step-by-step explanation:
The question pertains to geology, specifically the stratigraphy of the Grand Canyon. The youngest flat lying rock layer exposed along the walls of the Grand Canyon is the Kaibab Limestone. This rock formation lies atop the other layers, making it the most recent or youngest in the geological sequence visible in the canyon walls. Below the Kaibab Limestone lies the Toroweap Formation, below which is the Coconino Sandstone, followed by other layers.
It's essential to recognize that geological layers are typically oldest at the bottom and youngest at the top, due to the way sediment accumulates over time. The layers of the Grand Canyon provide an excellent record of Earth's geological history, which is visible in the Grand Canyon's cross-section displays and descriptions, such as those provided in visitor centers or educational resources.