Final answer:
The Plateau Indian cultures in Washington developed due to their access to natural resources, the development of permanent settlements near rivers and streams, and the introduction of horses to the area.
Step-by-step explanation:
The Plateau Indian cultures in Washington developed due to factors such as their access to natural resources, the development of permanent settlements near rivers and streams, and the introduction of horses to the area. The Plateau region was smaller and less populated compared to other Native American cultures, which allowed the people to rely on the abundant resources within their immediate vicinity for survival. Additionally, the adoption of horse riding and hunting enhanced their mobility and resource acquisition.