Mapping Mountains – Summit Relocations – Y Trichant – The 300m Hills of Wales

Mynydd Cefn Ddwy Graig (SH 936 340) 

There has been a Summit Relocation to a hill that is listed in the Y Trichant – The 300m Hills of Wales, with the summit height, bwlch height and their location, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Mynydd Cefn Ddwy Graig (SH 936 340)

The criteria for the list that this summit relocation applies to are:

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Mynydd Cefn Ddwy Graig, and it is adjoined to the Esgeiriau Gwynion group of hills, which are situated in the southern part of North Wales (Region A, Sub-Region A3), and it is positioned with the B4391 road to its north, the B4403 road to its west and a minor road to its south, and has the town of Y Bala towards the north north-west.

When the sub list was standardised and interpolated heights and drop values also included in the original Welsh 300m P30 list that was published on Geoff Crowder’s v-g.me website, this hill was listed with an estimated c 348m summit height positioned at SH 933 339, based on interpolation of its uppermost 340m ring contour. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Mynydd Cefn Ddwy Graig (SH 936 340)

The summit height produced by LIDAR analysis is 346.4m and is positioned at SH 93620 34020, and this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is judged to be a relatively recent man-made construct, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

Therefore, the summit height produced by LIDAR analysis is 346.4m and this is positioned at SH 93620 34020, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and is approximately 260 metres eastward from where the previously listed summit was given. 

 

The full details for the hill are:

Group:  Esgeiriau Gwynion 

Name:  Mynydd Cefn Ddwy Graig 

OS 1:50,000 map:  125

Summit Height:  346.4m (LIDAR)                                                           

Summit Grid Reference (New Position):  SH 93620 34020 (LIDAR) 

Bwlch Height:  317.8m (LIDAR) 

Bwlch Grid Reference:  SH 93117 33669 (LIDAR) 

Drop:  28.55m (LIDAR) 

 

Myrddyn Phillips (May 2022)