Related Link:  National landmarks threatened by climate change (USA Today)

On a bright, unseasonably hot morning in early May, Susan Meredith pushed her kayak off the banks of the Little Blackwater River, a shallow, 15-mile tributary running through Dorchester County, on Maryland's Eastern Shore. The water, cool and dark, is almost perfectly still, broken only by the occasional leaping fish.

Today, the quiet marshes provide refuge for wildlife -- ospreys, bald eagles, muskrats, the endangered Delmarva fox squirrel. But 160 years ago, it was people who sought refuge in these marshes, using the water, grasses, and trees as they fled slavery. Harriet Tubman, herself born into slavery in Dorchester County in the early 1820s, led dozens of African-Americans through this region to freedom in the North as part of the Underground Railroad.

The region remains largely unchanged from Tubman's time, save the paved roads, a few buildings and a distant cell phone tower. Tubman's grandmother, Modesty, lived on a farm across the street from where Meredith launched her kayak. "What you're looking at is what she looked at," said Meredith, owner, along with her husband, of Blackwater Paddle and Pedal. "What you're seeing, she saw."

In March 2013, President Barack Obama granted new protections for 11,750 acres here, with an executive order designating this as the Harriet Tubman Underground Railroad National Monument. The state of Maryland is building a new visitor center not far away, where people will be able to learn about this chapter of American history.

But sea level rise fueled by climate change threatens this flat, low-lying peninsula. The Tubman site, though one of the newest in the national park system, is also among those most at risk from climate change impacts. It's included in a report from the Union of Concerned Scientists, released Tuesday, that details risks posed by climate change to 30 cultural and historic landmarks across the country.