Are the Catskill Mountains Part of the Appalachians?

Technically, no—the Catskills are not part of the Appalachian Mountains proper (the folded, sedimentary ridge-and-valley province). Instead, they are a dissected plateau—the easternmost extent of the Appalachian Plateau Province (also called the Allegheny Plateau).

Key Distinctions

• Geology: Catskills = flat-lying Devonian sediments eroded into mountains; Appalachians = folded/faulted Paleozoic strata.
• Structure: Catskills are an uplifted, incised plateau; Appalachians are compressional orogenic belts.
• Location: Mostly in NY (Greene, Ulster, Delaware, Sullivan counties); small part in PA.
• Highest Peak: Slide Mountain (4,180 ft / 1,274 m) — lower than many Appalachian summits.

Colloquially, they're often grouped with "the Appalachians" in broad regional terms, but physiographically, they're a distinct province west of the true Appalachian Mountains.