Final answer:
The volunteer unit among the troops on Cuba's mainland during the Spanish-American War was called the Rough Riders.
Step-by-step explanation:
The volunteer unit that was among the 17,000 troops stationed on Cuba's mainland during the Spanish-American War was called the Rough Riders. The Rough Riders were an all-volunteer cavalry unit led by Theodore Roosevelt. They were made up of adventure-seeking college graduates, veterans, and cowboys from the Southwest.