Since the 1950s, its application has become increasingly localised to the geographically homogeneous Mid Wales uplands, known in Welsh as Elenydd, which extend from Plynlimon (Pumlumon) to Radnor Forest in the east and Mynydd Mallaen to the south.

The ranges of mid-Wales on the other hand are predominantly formed from Ordovician and Silurian sandstones and mudstones which in many areas outcrop only infrequently so resulting in more rounded grassy hills.

Cefn Croes, the site of a controversial wind farm project, is in the Cambrian Mountains, just south of the A44 road between Aberystwyth and Llangurig.

Despite continuing local opposition, the Countryside Commission published the order designating the area on 15 August 1972, and submitted it to the Secretary of State for Wales, Peter Thomas, for confirmation.

In July 1973, the Secretary of State announced the decision not to proceed with the designation because of "massive evidence of objections", and also rejected a call to hold a public inquiry.