The land under the bridge is part of the Tennessee Hollow Watershed. The water flows from a freshwater spring down the side of a mountain and trickles through this grassy area.
When the US Army drained this "swamp" to create dry land for a shooting range and other uses, the water was channeled into culverts and carried underground to its ultimate destination, San Francisco Bay.
When the Presidio Trust daylighted the water, the native plants returned, creating habitat for native frogs, insects and birds. It's a lively place.
It got its name from the 1st Tennessee Regiment, volunteer soldiers who camped here before shipping out to the Philippines for the Spanish-American War.