Final answer:
Elephant Butte Reservoir is located on the Rio Grande river and serves as a key water resource in the southwestern United States.
Step-by-step explanation:
Elephant Butte Reservoir is located on the Rio Grande river. It is a major reservoir which was created by the construction of a dam to provide water for various uses. Historically and geographically significant, the reservoir continues to serve the southwestern region of the United States.
Although it was not part of the Salt River Project led by President Theodore Roosevelt, it is an example of early 20th-century efforts to manage water resources in arid regions of the United States, similar to the dams built on the Salt River.