The Lost River is so-named because the brook draining the southern part of Kinsman Notch disappears below the surface in a narrow, steep-walled glacial gorge. The gorge is partially filled with immense blocks of granite, through the spaces of which the brook cascades along its subterranean course until it eventually emerges and joins the Pemigewasset River, which flows southward from Franconia Notch.
Crawling through one of the gorge's most narrow caves
Lost River Reservation protects 157 acres (64 ha) around the gorge and is owned by the Society for the Protection of New Hampshire Forests.[1] Admission to the gorge is by fee.[2] There are stairs down to the gorge area, with a 3⁄4 mile (1.2 km) boardwalk along the gorge. Most caves can be walked or crawled into.
The Forest Society maintains two free trails on the Lost River Reservation, which are separate from the gorge area leased to White Mountain Attractions.