The Catskills had already been displaced as New York's highest mountains by the Adirondacks‘ Mount Marcy and other High Peaks there; in 1879 Princeton geology professor Arnold Guyot, a regular summer guest at the Mountain House since the Civil War, announced that not only were the so-called "Shandaken Mountains" in Ulster County to the southwest geologically continuous with the Catskills, one of them, Slide Mountain, was at 4180 feet the highest peak in the entire range, instead of the Escarpment's Kaaterskill High Peak.