Final answer:
The most extensive type of rocks in the United States based on the map of rock distribution is sedimentary rocks.
Step-by-step explanation:
The map of rock distribution in the United States clearly shows that sedimentary rocks are the most extensive type. Sedimentary rocks are formed from the accumulation and cementation of sediments, such as sand, mud, and organic matter. They cover the surface and overly older rocks throughout North America, and they can be of all geologic ages and deposited in paleoenvironments different from what exists in the region today.