 The Ice Age brought glaciers more than a mile thick that grounded, lifted, and deposited rocks that formed notches and mountains. When the ice melted, the water carried debris, eroding the rocks and forming Lost River Gorge. Lost River is so named because the brook draining from the southeast part of Kingsman Notch disappears below the surface in a narrow, steep-walled glacier gorge. The brook cascades along its subterranean course until it eventually merges with the Pemichawasset River.