Its northern boundary is, for the most part, formed by Lake Ontario and the St Lawrence river, which separate it from the province of Ontario, Canada; but north of the Adirondacks the boundary line leaves the St Lawrence, extending in a due east direction to the lower end of Lake Champlain.
From the crest of the dome of the Adirondacks proper the surface slopes in all directions to surrounding lowlands: to the St Lawrence valley on the N.; the ChamplainHudson lowland on the E.; the Mohawk valley on the S.; and Lake Ontario on the W.
Like the Adirondacks, this region is largely forest covered, and is a favourite summer resort; but it is far less a wilderness than the Adirondacks, and in places is cleared for farming, especially for pasturage.
After the continental ice sheet entirely disappeared from the state, local valley glaciers lingered in the Adirondacks and the Catskills.
It occupies the lower portion of the trough between the Adirondacks and the Green Mountains.