Mapping Mountains – Hill Reclassifications – Y Trechol – The Dominant Hills of Wales

Ynys Gron (SH 596 392) - Dominant deletion

There has been a deletion to the listing of Y Trechol – The Dominant Hills of Wales due to detail included on current Ordnance Survey maps.  This has resulted in the hill being taken out of the Dominant list.  With the criteria for inclusion to this list being those Welsh P30 hills whose prominence equal or exceed half that of their absolute height.

The details relating to this hill’s deletion as a Dominant hill are retrospective as it did not appear in the Moelwynion group of hills when published on Mapping Mountains on the 25^th February 2016.

The hill had been listed in the original Welsh P30 lists when published on Geoff Crowder’s v-g.me website with a 96m summit height based on the Ordnance Survey 1:25,000 Outdoor Leisure spot height, with an accompanying note stating ‘98m on 1984 1:50,000 map.  Summit being reduced due to quarrying’.  When drop values were added to the P30 Master Lists this hill was given an estimated drop of c 50m which gave the hill 52.08% Dominance, and therefore it was included in the original listing of Y Trechol – The Dominant Hills of Wales.

The hill is in the Moelwynion group of hills and is placed in the Region of North Wales (Region A, Sub-Region A1) and is situated between the towns of Porthmadog to the west and Penrhyndeudraeth to the east, and immediately above the busy A 487 road which is to its south.

The hill is not on open access land and its whole south-western part forms the Garth Quarry, which is operational, because of this permission to visit should be sought.  However, the approach from the east is through woodland and would take a visitor direct to the remaining high point of the hill.

The name of the hill is Ynys Gron, which is a locally known name and it has been deleted from the Dominant list as the quarry has now obliterated the upper 30m of the hill and reduced it in height to 69.4m (converted to OSGM15), and as its bwlch has been surveyed as 44.3m (converted to OSGM15) in height, it gives this hill only 25.1m of drop, which is insufficient for it to be considered for Dominant status.

The full details for the hill are:

Group:  Moelwynion

Name:  Ynys Gron

Dominance:  N/A

OS 1:50,000 map:  124

Summit Grid Reference:  SH 59653 39268

Summit Height:  69.4m (converted to OSGM15)

Drop Summit to Bwlch:  25.1m

Drop Bwlch to ODN:  44.3m (converted to OSGM15) 

The view west from the summit of Ynys Gron

 For details on the survey that confirmed this hill’s lack of Dominance

Myrddyn Phillips (April 2017)