Forming the southern and eastern edge of the Ridge-and-Valley Appalachians physiographic province in Pennsylvania, Blue Mountain extends 150 miles (240 km) from the Delaware Water Gap on the New Jersey border in the east to Big Gap in Franklin County in south-central Pennsylvania at its southwestern end.

Views of Blue Mountain dominate the southern tier of most eastern and central Pennsylvania counties, providing an ever-visible backdrop cutting across the northern or western horizon.

The barrier ridge forms a distinct boundary between a number of Pennsylvania's geographical and cultural regions.

To the south of Blue Mountain lies the Capital Region of Harrisburg and nearby communities, the rich farming country of the Lebanon Valley and Pennsylvania Dutch Country of York and Lancaster counties, the lower half of the Lehigh Valley, and the lower Delaware Valley, both of which extend north through water gaps beyond the ridgeline.

Mount Minsi, elevation 1,461 feet (445 m), forms the promontory overlooking the Delaware River.