Final answer:
The correct answer is Option 2: Securing freshwater sources for military installations, including Zebulon Pike.
Step-by-step explanation:
Finding the headwaters of Oklahoma's rivers was important to the United States' national security for several reasons. One reason was the need to secure freshwater sources for military installations, which played a critical role in maintaining the country's defense capabilities.
Another reason was preventing river-based invasions from hostile forces, as controlling the headwaters would give the United States a strategic advantage in defending its territories. Some of the men who searched for the headwaters of Oklahoma's rivers include Zebulon Pike and John C. Frémont.