The Fen

Just west of the Happy Isles Nature Center, a narrow boardwalk carries you across one of the rarest habitats in Yosemite Valley: The Fen, a peat-forming wetland kept wet year-round by groundwater rather than rainfall. In a landscape defined by bone-dry Sierra summers, that makes it a genuine outlier — a pocket of sedges, ferns, and standing water at the base of Glacier Point.

What Makes a Fen Different

Unlike a bog, which relies on rainfall, a fen is fed by moving groundwater — here, snowmelt draining down the granite face of Glacier Point keeps the soil saturated even in late summer. The wetland supports horsetails, lady ferns, and sedges uncommon elsewhere in the park, along with song sparrows, tree frogs, and butterflies drawn to the reliable moisture. Interpretive signs along the boardwalk explain the ecology as you go.

Getting There

The Fen sits just off the Happy Isles shuttle stop, a short walk from the trailhead for the Mist Trail and Vernal/Nevada Falls. The boardwalk itself runs about 2,100 feet — roughly a 7-minute walk one way — and is wheelchair accessible. Boards get slick when wet or icy, and the area can flood during peak spring snowmelt, so plan around conditions.

A Wetland With a History

The fen originally covered about three acres in two separate arms. In 1928 the Park Service filled the eastern arm with river sand to build a parking lot; ecological restoration work in 2002 recovered much of what remained. What's left today is a small but genuinely rare slice of Sierra wetland, worth the few minutes it takes to walk through.