Penmoelallt

Penmoelallt or Onllwyn is a hill in the northern part of the county borough of Rhondda Cynon Taff in south Wales.

To the west is the hill known as Mynydd-y-glog and to the south are slopes draining into the River Taff and the Afon Cynon.

Its afforested nature makes it difficult to determine the precise location of its highest point but this probably lies somewhere around OS grid ref SO 003096.

Above these are the coarse sandstones of the Twrch sandstone (formerly the 'Basal Grit') of the Marros Group (former 'Millstone Grit Series') whilst the southernmost slopes are formed in the lowermost beds of the Lower South Wales Coal Measures.

Much of the bridleway between Ffrwd Uchaf and Pen-twyn-isaf serves as a forest track and provides ready access from Cwm Taf, as does the footpath which carries the Taff Trail between the same locations.