Tuesday, 21 March 2017

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


Pt. c 71m (SH 310 297) - Lesser Dominant addition

There has been an addition to the listing of Y Trechol – The Dominant Hills of Wales due to detail included on the Ordnance Survey enlarged mapping hosted on the Geograph website.  This has resulted in the hill being added to the Lesser Welsh Dominant list.  The criteria for Lesser Welsh Dominant status is those P30 hills whose prominence is 33% or more and below 50% of their absolute height.

The details relating to this hill’s inclusion as a Lesser Welsh Dominant hill are retrospective as it appeared in the Pen Llŷn group of hills when published on the Mapping Mountains site on the 11th February 2016.

Prior to this hill’s inclusion as a Lesser Welsh Dominant hill it was listed with c 25m of drop which is insufficient for consideration to this sub category of hill, with this drop value based on an estimated summit height of c 71m based on the size of the uppermost 70m ring contour on Ordnance Survey maps in comparison to the size of contours below it, and an estimated bwlch height of c 46m based on bwlch contouring between 40m – 50m that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.   

The hill is listed in the Pen Llŷn group and is placed in the Region of North Wales (Region A, Sub-Region A1) with its Cardinal Hill being Garn Fadrun (SH 278 351), and it is situated between the small communities of Llanbedrog to the north-east, Mynytho to the north-west and Abersoch to the south.

If wanting to visit the hill permission to do so should be sought as the summit area is not a part of open access land, however the hill has a number of public footpaths encircling it that start from the A 499 road to its east and the network of minor roads to its north and west.

The hill is being listed by the point (Pt. c 71m) notation as an appropriate name either known locally or from historical research has not been found by the author, although when the hill was first included in the P30 Welsh lists that appeared on Geoff Crowder’s v-g.me website it was by an invented name of Castellmarch, this name was taken from buildings situated to the east of the summit.

It is included as a Lesser Welsh Dominant hill as the Ordnance Survey enlarged mapping hosted on the Geograph website has contours at 5m intervals giving the hill a 41m bwlch spot height with bwlch contouring between 40m – 45m, as opposed to the previously estimated bwlch height of c 46m based on the 40m – 50m bwlch contouring on the 1:25,000 Explorer map.  With an estimated c 71m summit height and a 41m bwlch height it gives this hill c 30m of drop which is sufficient for consideration to the Dominant list, and as these values give this hill 42.25% Dominance it is now listed as a Lesser Welsh Dominant hill.


The full details for the hill are:

Group:  Pen Llŷn

Name:  Pt. c 71m

Dominance:  42.25%

OS 1:50,000 map:  123

Summit Grid Reference:  SH 31034 29730

Summit Height:  c 71m

Drop Summit to Bwlch:  c 30m

Drop Bwlch to ODN:  41m 



Myrddyn Phillips (March 2017)











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