Final answer:
The most common buildings in the U.S. Southwest were adobe houses, which were made of sun-dried mud bricks. These multi-room structures had flat roofs and were popular among both Spanish settlers and indigenous people.
Step-by-step explanation:
In the U.S. Southwest, the most common buildings were adobe houses. These houses were made of sun-dried mud bricks and were popular among both Spanish settlers and indigenous people of the region. The houses were typically multi-room structures with flat roofs that could be used as terraces. Some notable examples of these buildings include Pueblo Bonito in New Mexico, Cliff Palace in Colorado, and Casas Grandes in Chihuahua.